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COF/RIGHT DEPOSm 



THE NUTRITION OF FARM ANIMALS , 



•The 




THE MACMILLAN COMPANY 

NEW YORK • BOSTON - CHICAGO • DALLAS 
ATLANTA ■ SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY • CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



THE NUTRITION 

OF 

FARM ANIMALS 



BY 



HENRY PRENTISS ARMSBY, Ph.D., LL.D. 

DIRECTOR OF THE INSTITUTE OF ANIMAL NUTRITION OF THE 
PENNSYLVANIA STATE COLLEGE; EXPERT IN ANIMAL 
NUTRITION, UNITED STATES DEPARTMENT OF 
AGRICULTURE; FOREIGN MEMBER, 
ROYAL ACADEMY OF AGRICUL- 
TURE OF SWEDEN 



THE MACMILLAN COMPANY 
1917 

All rights reserved 



,0 






Copyright, 1917, 
By THE MACMILLAN COMPANY. 



Set up and electrotyped. Published June, 1917. 



JUN 21 1917 



Nortooofi $regs 

J. S. Cushing Co. — Berwick & Smith Co. 

Norwood, Mass., U.S.A. 



©GI.A470024 



PREFACE 

The manner in which the subject of the nutrition of farm 
animals is presented to the student will naturally differ ac- 
cording to the ultimate end in view. If the prime purpose is 
to impart practical skill in the feeding of live stock, the study 
of the principles of nutrition is likely to be regarded as pre- 
liminary and to partake of the nature of an information course, 
and chief stress will be laid upon familiarity with the results 
of experience, particularly as related to the business aspects 
of the subject, and to the acquisition of practical skill. 

But while by no means disposed to minimize the significance 
of this aspect of the subject, the writer is nevertheless convinced 
that for the students of our agricultural colleges a somewhat 
different procedure is desirable. He believes that greater 
emphasis than they sometimes receive may wisely be laid upon 
the chemical and physiological laws which underlie the practice 
of feeding, both on account of their intrinsic importance and 
because the subject may thus be made a real collegiate disci- 
pline which shall contribute to the training as well as to the 
information of the student. 

Accordingly, the present volume attempts to deal primarily 
with the natural laws governing the nutrition of farm animals, 
as distinguished from the broader field of animal husbandry, 
and only secondarily with the specific details of practice. It 
seeks to avoid so far as may be mere dogmatic statements, and, 
although not attempting complete citation of literature even 
upon important points, to present the experimental evidence 
with sufficient fullness to indicate something of the limitations 
of present knowledge and of trie* opportunities for further in- 
vestigation. Its aim is to discuss the fundamental principles 
upon which successful stock feeding is consciously or uncon- 
sciously based in the firm persuasion of the truth so pithily 
expressed almost half a century ago by the father of agricul- 
tural science in the United States, Professor Samuel William 



V i PREFACE 

Johnson, that, "Other qualifications being equal, the more 
advanced and complete the theory of which the farmer is the 
master, the more successful must be his farming. The more he 
knows, the more he can do. The more deeply, comprehen- 
sively, and clearly he can think, the more economically and 
advantageously can he work," and that "A true theory is the 
surest guide to a successful practice." 

In short, the book is intended for the student rather than 
directly for the farmer and assumes a certain degree of prelim- 
inary training on the part of the reader, including an elementary 
knowledge of chemistry and physics. 

The author is under obligations to The Honorable Secretary 
of Agriculture, for permission to reproduce, in Chapter XVIII, 
a part of Bulletin No. 459 of the United States Department of 
Agriculture ; to the Macmillan Company for the similar use in 
Chapter XV of material from Bailey's " Cyclopedia of American 
Agriculture"; and to Messrs. Henry and Morrison for permis- 
sion to base the tables of the net energy values of feeding stuffs 
contained in the Appendix upon their extensive compilations 
in the fifteenth edition of " Feeds and Feeding." He is like- 
wise indebted to the following publishers for the use of the cuts 
named : 

The Carnegie Institution of Washington, Figure 24. 

The F. A. Davis Company, Figure 17. 

Ginn & Company, Figures 2, 3, 6, 7, 8, 16, 19, 20, and 22. 

The Macmillan Company, Figures 4, 15, 29, 31, 32, ^3> 34, 
37, 43, 44, and 45. 

The W. B. Saunders Company, Figures 1,5, and 14. 

John Wiley & Sons, Inc., Figures 18 and 40. 

State College, Pa., 
May, 191 7. 



CONTENTS 



Introduction 



PAGE 

vii 



PART I 
THE MATERIALS OF NUTRITION 



CHAPTER I 

The Components of Plants and Animals 
§ i. Dry matter; organic matter; ash 
§ 2. The carbohydrates 



§ 3. Fats and related bodies 

§ 4. The proteins . 

§ 5. The non-proteins . 

§ 6. Sundry ingredients 



The Lipoids 



CHAPTER II 

The Composition of Animals and of Feeding Stuffs 

§ 1. The cell 

§ 2. Animal tissues and organs 

§ 3. The composition of the animal as a whole . 
§ 4. The composition of feeding stuffs . 



3 

3 
7 
16 
24 
36 
39 



42 
42 

45 
61 
66 



PART II 
THE PROCESSES OF NUTRITION 



CHAPTER III 

Digestion and Resorption . . 
§ 1. The organs of digestion 
§ 2. The chemistry of digestion . 
§3. Resorption — The feces 
§ 4. The determination of digestibility 

vii 



77 
77 
89 

105 
in 



Vlll 



CONTEXTS 



CHAPTER IV 

PAGE 

Circulation, Respiration, and Excretion 123 

§ 1. Circulation 123 

§ 2. Respiration . 132 

§ 3. Excretion 139 



CHAPTER V 



Metabolism 

§ 1. General conception 
§ 2. Enzyms as agents in metabolism . 
§ 3. The metabolism of the carbohydrates 
§ 4. The metabolism of the simple proteins 
§ 5. The metabolism of the nucleoproteins 
§ 6. The metabolism of the fats . 
§ 7. Metabolism of ash ingredients 
§ 8. Functions of the nutrients 



144 
144 
148 

152 
160 
168 
171 
178 
182 



CHAPTER VI 



The Balance of Nutrition . 
§ 1. General conception 
§ 2. Methods of investigation 
§ 3. The balance of matter . 
§ 4. The balance of energy . 
§ 5. Significance of results . 



192 
192 
194 
202 
216 
241 



PART III 



THE FEED REQUIREMENTS 



CHAPTER VII 



The Fasting Katabolism 

§ 1. The protein katabolism in fasting 

§2. 

§3- 



The energy katabolism in fasting . 
Conditions affecting the fasting katabolism 



249 

251 
256 

258 



CONTENTS ix 



CHAPTER VIII 

PAGE 

Maintenance — The Energy Requirements . . . .267 

§ 1. Net energy values for maintenance 271 

§ 2. Maintenance requirements of farm animals . . . .280 
§ 3. Factors affecting the maintenance requirement . . . 304 
§ 4. The relation of the maintenance requirement to external 

temperature 308 

CHAPTER IX 

Maintenance (Continued) — The Requirements of Matter . 313 
§ 1. The protein requirements for maintenance . . . .313 
§ 2. The ash requirements for maintenance . . . . .332 
§ 3. Accessory substances 348 

CHAPTER X 

The Fattening of Mature Animals 350 

§ 1. Composition of the increase in fattening . . . .350 
§ 2. Feed requirements for fattening 359 

CHAPTER XI 

Growth 371 

§ 1. General nature of growth 371 

§ 2. The utilization of feed in growth 381 

§ 3. The feed requirements for growth 396 



CHAPTER XII 

Meat Production . 

§ 1. Nature of meat production . 

§ 2. The animal as a factor in meat production 

§ 3. Feeding for meat production 

§ 4. Influence of external conditions . 



CHAPTER XIII 

Milk Production 

§ 1. The physiology of milk production 

§ 2. The animal as a factor in milk production . 

§ 3. The influence of environment on milk production 

§ 4. The utilization of feed in milk production 

§5. Feeding. for milk production . 



424 
424 
428 
444 

453 



459 
459 

470 

478 
488 
500 



X CONTENTS 

CHAPTER XIV 

PAGE 

Work Production 531 

§ 1. The physiology of work production 531 

§ 2. The efficiency of the body as a motor 544 

§ 3. Feed requirements for work 560 



PART IV 

THE FEED SUPPLY 

CHAPTER XV 

The Feeding Stuffs 571 

§ 1. Roughages, or coarse fodders 572 

§ 2. Roots, tubers and fruits 578 

§ 3. The concentrates 579 



CHAPTER XVI 

Relative Values of Feeding Stuffs 591 

§ 1. Direct comparisons of feeding stuffs 591 

§ 2. Relative values based on composition and digestibility . 597 

§ 3. Conditions affecting digestibility 601 



CHAPTER XVII 

The Production Values of Feeding Stuffs 

§ 1. General considerations 

§ 2. Production values as regards energy — Net energy values 
§ 3. The computation of net energy values .... 
§ 4. Production values as regards protein .... 



CHAPTER XVIII 



630 
630 

634 
667 
678 



The Computation of Rations 689 

§ 1. Feeding standards 689 

§ 2. Feed requirements 691 

§ 3. Method of computation 697 



CONTENTS 



XI 



APPENDIX 



Estimated Protein and Energy Requirements of Farm Animals 



Table I. 



Table II. 



Table III. 



Table IV. 

Table V. 
Table VI. 



Maintenance requirements of cattle and horses, 
per day and head 

Maintenance requirements of sheep and swine, per 
day and head 

Requirements for fattening with no considerable 
growth — all species — in addition to the 
maintenance requirement .... 

Requirements for growth with no considerable fat- 
tening 

Requirements for milk production .... 

Requirements for work production by the horse 



Average Dry Matter, Digestible Protein and Net Energy 
Values of Feeding Stuffs per ioo Pounds 

Table VII. Values per ioo pounds for ruminants 
Table VIII. Values per ioo pounds for the horse 
Table IX. Values per ioo pounds for swine .... 
Table X. Mineral elements of feeding stuffs — per ioo 
pounds of dry substance 



PAGE 

711 

711 
711 

712 

712 
7i4 
7i4 

7i4 

7i5 
721 

722 

723 



REFERENCES 

The full-face numbers in parenthesis in the body of the text refer to 
the numbered paragraphs and not to pages. 



ILLUSTRATIONS 



FIG. 

i. Different types of cells composing the body 

2. One end of a muscle fiber . 

3. Part of a muscle fiber . . . . . 

4. Fat cells in muscles ...... 

5. Scheme of a fat cell 

6-8. Successive stages in the formation of adipose tissue 

9. Sheep's stomach ' 

10. Stomach and duodenum of horse .... 

11. Stomach of hog ....... 

12. Intestines of cattle 

13. Ccecum of horse . . . . . 

14. Section of villi 

15. Steer in digestion stall 

16. Blood corpuscles 

17. Diagram of mammalian heart .... 

18. Scheme of circulation of blood .... 

19. Relation of cells to blood vessels and lymphatics 

20. Main lymphatic trunks 

21. Alveoli of lung 

22. Section of two alveoli 

23. Diagrammatic scheme of metabolism . 

24. Scheme of closed-circuit respiration apparatus . 

25. Original Regnault-Reiset apparatus 

26. Regnault-Reiset apparatus as used by Zuntz 

27. Scheme of Pettenkofer respiration apparatus 

28. Pettenkofer respiration apparatus, explanatory sketch 

29. The Mockern respiration apparatus 

30. Horse equipped for experiments with Zuntz apparatus 

31. Lavoisier's ice calorimeter ..... 

32. Section of bomb calorimeter .... 
^^. The Zuntz tread power dynamometer . 

34. Dulong's water calorimeter 

35. The respiration calorimeter at The Pennsylvania State 

36. Rubner's calorimeter 

37. The marbling of meat ...... 

38. Rate of gain of protein per 1000 pounds live weight 

xiii 



College 



PAGE 

43 
50 
5i 
52 

58 

59 

80 

81 

81 

84 

85 

105 

113 

124 

125 
127 
130 
131 
133 
133 
182 
209 
210 
211 
213 

213 
214 

215 
222 
224 
226 

237 
238 

239 
356 
379 



XIV 



ILLUSTRATIONS 



39." Rate of gain of energy per 1000 pounds live weight 

40. Lobule of milk gland . 

41. Alveoli of milk gland . 

42. Structure of milk gland 

43. Partial section of wheat grain 

44. Partial section of oat grain . 

45. Partial section of maize kernel 



398 
462 

463 
463 
582 

584 
588 



INTRODUCTION 

The problems of nutrition concern the farmer both directly 
and indirectly — indirectly because his function in society is to 
furnish the materials for the nutrition of man ; directly, because 
an essential part of that function consists in the economical 
conversion of vegetable into animal products by means of farm 
animals. Particularly is this true regarding the inedible prod- 
ucts of the farm. It is a well-recognized fact that only the 
smaller portion of the solar energy or of the proteins which are 
stored up in the farmer's crops is directly available for man's 
use. Even in distinctively food crops, such as wheat, for ex- 
ample, more than two-thirds of the energy which they contain 
may be unavailable for human nutrition, while the grasses and 
legumes, so important in all systems of agriculture, are of no 
direct value as food for man. The essential function of the 
animal in a permanent system of agriculture is the conversion 
of as large a proportion as possible of these inedible products 
into forms whose matter and energy can be utilized by the 
human body. It is true that animal products contribute largely 
to our supply of clothing and also that, as a motor, the work 
animal plays an important part in agriculture and industry. In 
both respects, however, substitution is possible to a greater or 
less extent. Vegetable fibers may to a degree replace animal 
fibers in our textiles, while inanimate motors seem destined to 
fill an increasing role in power production in all its aspects. 
But for the conversion of the by-products of the farm and fac- 
tory into human food, there is as yet no suggestion of an agency 
which can take the place of the animal body. 

With the growth of the non-agricultural population it is in- 
creasingly important that this function of conserving the food 
supply through the utilization of inedible soil products shall be 
performed with a maximum of efficiency. This requires, on the 
one hand, as intimate a knowledge as possible of the funda- 
mental laws governing the nutrition of farm animals, so that 

XV 



xvi INTRODUCTION 

the transformation may be effected with the least possible waste, 
and, on the other hand, the ability so to apply these laws as to 
secure the greatest economic return, since it must never be 
forgotten that the criterion of success in agriculture is not a 
maximum production but a maximum profit. It is with the 
former portion of this complex problem that the present work 
attempts primarily to deal. 

Without entering into the controversy between the vitalist 
and the mechanist, the nutrition of the animal, whatever its 
guiding principle, may be regarded as a physico-chemical pro- 
cess, including the entire complex of reactions by which the 
crude materials of the feed are converted into substances suited 
to maintain the activities of the body cells or capable of being 
built up into living structures. In other words, the study of 
nutrition is a study of the chemistry and physics of the changes 
through which the crude products of the soil yield animal tissues 
or secretions on the one hand and excretory products on the 
other. 

The earlier investigators dealt with the food as a supply of 
matter, dividing it into inorganic and organic constituents and 
distinguishing among the latter between the nitrogenous and 
non-nitrogenous substances. In other words, they studied the 
problems of nutrition substantially as problems of biological 
chemistry. Rubner's fundamental investigations went far to 
shift the emphasis to the physical side of the problem. It has 
come to be clearly recognized that the animal body is essen- 
tially a transformer of energy — a mechanism for the conversion 
of the chemical energy of its feed into motion energy while 
more or less incidentally a reserve of energy-containing material 
may be stored up which can be utilized for human food. It is 
this capacity of the animal body to store up in itself or in its 
secretions a part of the matter and energy of the feed it con- 
sumes which gives the animal its economic significance as a 
conserver of the food supply. Its value in this respect depends 
upon the proportion of its feed which it is able thus to set 
aside — i.e. upon the balance between the income and outgo 
of matter and of energy — and it is from this point of view that 
the present volume undertakes to present the nutrition of farm 
animals. From this standpoint, the subject naturally falls into 
four principal divisions. 



INTRODUCTION xv j{ 

First, since nutrition involves chemical changes by which 
feed substances are converted into body substances, there is 
required some knowledge of the chemical compounds concerned 
and of their occurrence and proportions in plants and animals. 

Second, the conversion of feed substances into body sub- 
stances is a function of the living organism and it becomes 
necessary, therefore, to learn something of the processes by 
which the body effects these changes or, in other words, to 
study the physiology of nutrition. 

Third, in order to apply the principles of the chemistry and 
physiology of nutrition to the practical problems arising in the 
feeding of farm animals it is requisite to determine quantita- 
tively the amounts of matter and of energy which are required 
by different species of animals for their support and for the 
production of meat, milk or work. 

Fourth, to supply the feed requirements as thus ascertained 
in the most economical manner demands a knowledge of the 
available feed resources, both as to the nature and quantity of 
nutriment which they contain and as to the proportion of this 
nutriment which can be utilized by the body. 

Accordingly, the general subject of the nutrition of farm ani- 
mals is treated of under four general heads, viz. : — 

Part I, The Materials of Nutrition. 
Part II, The Processes of Nutrition. 
Part III, The Feed Requirements. 
Part IV, The Feed Supply. 



PART I 
THE MATERIALS OF NUTRITION 



NUTRITION OF FARM 
ANIMALS 

CHAPTER I 

THE COMPONENTS OF PLANTS AND ANIMALS 

§ i. Dry Matter; Organic Matter; Ash 

1. Dry matter. — The material composing the plant or 
animal may be regarded as consisting of water and dry matter. 
The two are ordinarily separated by maintaining the material 
at or above the boiling point of water until it ceases to lose 
weight. The loss in weight is regarded as consisting solely of 
water, while the residue is, of course, the dry matter. 

2. Water. — Water is by no means to be regarded as an 
accidental or incidental component of plants or animals. The 
necessity for an adequate water supply to living beings is too 
well known to require mention, while very little reflection is 
needed to show that the water is as essential a part of the organ- 
ism as any other ingredient. In the supporting tissues of the 
plant or animal it has a mechanical function, lending elasticity 
combined with strength. It acts as a solvent and carrier of 
food materials and waste products and the osmotic pressures 
of the solutes are an important factor in physiological processes. 
Finally, its action in dissociating electrolytes appears to be 
very intimately related to the chemistry of living matter. 

Water is usually abundantly supplied to live stock. The 
study of animal nutrition, therefore, deals chiefly with the dry 
matter, its supply and transformations, not because this is 
fundamentally any more essential than the water but because 
ordinarily it is economically more important. 

3 



4 NUTRITION OF FARM ANIMALS 

3. Organic matter. — By the action of oxygen at a high tem- 
perature, the dry matter of plants or animals may be separated 
into two portions, one being converted into the gaseous state, 
while the other remains behind in the solid form. Following 
the older nomenclature, it is customary to distinguish these 
two portions as " organic " and " inorganic," or " ash," in- 
gredients. The terms, however, are to some extent misnomers, 
since no such sharp distinction exists as was once supposed 
between organic and inorganic compounds. Organic matter 
in the sense in which the term is commonly used may be said 
to be broadly equivalent to the carbon compounds of the organ- 
ism, but even this definition is inexact and the same element 
may be volatilized during oxidation or may appear in the ash 
according to circumstances. 

For example, the element sulphur is an essential ingredient 
of the proteins. When these are burned in air part of the 
sulphur escapes in the gaseous form, but a part also combines 
with any bases present and appears in the ash as sulphates. 
Even the element carbon, distinctive of so-called organic matter, 
may appear in part in the ash of the plant or animal in the form of 
carbonates when the bases of the ash are in excess of the acid 
radicles. These examples serve to show that an element may 
be an integral part of the molecules which make up the organic 
matter and yet appear after incineration in the ash. Thus it 
has recently been shown that the phosphorus of wheat bran 
and other feeding stuffs is present chiefly in the form of a 
complex carbon compound, yet when these materials are burned 
the phosphorus appears in the ash in the form of phosphates. 

Organic matter is usually regarded as consisting of the ele- 
ments carbon, hydrogen, oxygen, nitrogen and sulphur, phos- 
phorus being sometimes added to the list, but doubtless other 
elements like potassium, sodium, chlorin, etc., also enter into 
the structure of the " organic " molecules. 

4. Subdivision of organic matter. — The number of individ- 
ual organic compounds found in the animal body or in the plant 
is very great. For the present purpose, however, it is not 
necessary to consider separately each individual substance but 
only the general properties of the important groups into which 
they may be classified. 

The organic constituents of the body may be subdivided into 



THE COMPONENTS OF PLANTS AND ANIMALS 5 

non-nitrogenous and nitrogenous substances. Under the former 
are included the carbohydrates, the fats, the organic acids and 
various other minor groups. The nitrogenous substances in- 
clude the proteins and a variety of simpler nitrogenous sub- 
stances sometimes classed together as the non-proteins. In the 
following sections these various groups will be considered as 
far as is requisite for an intelligent study of their behavior in 
the animal body, it being assumed that the reader has already 
some knowledge of their general properties, both chemical and 
physical. 

5. Mineral matter, or ash. —To what extent the elements 
found in the ash and commonly reckoned as the mineral ele- 
ments, namely, potassium, sodium, calcium, magnesium, iron, 
phosphorus, sulphur, chlorin, silicon, etc., are actually present 
in the living plant or animal as electrolytes and to what extent 
as ingredients of complex organic molecules, it is at present im- 
possible to state with any definiteness. In ordinary usage the 
term ash is equivalent to the residue remaining after incineration 
at as low a temperature as possible, usually not exceeding a 
dull red heat. 

The proportion of ash in ordinary feeding stuffs varies con- 
siderably according to the kind of plant, the portion of the plant 
used (seeds, stems, leaves, roots, etc.), the maturity of the 
plant and various other conditions. Wolff gives the following as 
general averages for the proportion of ash in the dry matter : — 




Cereal crops . 
Leguminous crops 
Oil plants . . . 



The proportion varies most in the straw and least in the grain. 
In the animal, the presence of ash is most evident in the bones. 
About two-thirds of the dry matter of the clean bone (free from 
fat) consists of ash. Ash is by no means absent from the soft 
tissues of the body, however, of which it forms an essential in- 
gredient. The proportion varies in different organs, but as 
a rough general average the body, inclusive of the skeleton, 
contains about 3.5 per cent of ash in the fresh substance, 



6 NUTRITION OF FARM ANIMALS 

equivalent to about 7.1 per cent of the dry matter. The pro- 
portion of ash to dry matter is greater in the young than in the 
mature animal and greater in the lean than in the fat condition. 
The more important elements found in the ash are as fol- 
lows: — 

Potassium. — This metal is indispensable to plant growth and is 
found in all parts of the plant, but especially in the active, growing 
parts. In the animal body it is found abundantly in the tissues, such 
as the muscles, glands, nerves, etc., while the fluids (blood, plasma, 
lymph, etc.) contain relatively small amounts of it. 

Sodium. — Unlike potassium, sodium is not indispensable to plant 
growth, although it apparently is useful to the plant under some con- 
ditions. It is found especially in the stems and leaves of plants, 
although not so abundantly as potassium. Seeds contain but little 
of it. In the animal body it is especially abundant in the fluids, 
which, as just noted, contain relatively little potassium. 

Calcium. — Like potassium, calcium is necessary for the growth 
of plants. It is found especially in the leaves and stems of plants 
and to a much less extent in the seeds. It appears to be equally 
essential to the animal and is found in all parts and organs of the body. 
Its most striking use, however, is in the formation of the skeleton, the 
mineral portion of which (81) consists chiefly of calcium phosphate 
and carbonate. Both these compounds being scarcely at all soluble 
in water, they are well adapted to form the framework of the body. 
In the skeletons of the higher animals calcium phosphate is the chief 
mineral ingredient, while in the lower animals like shellfish and 
Crustacea, the shell, which corresponds to the bones of domestic ani- 
mals, contains chiefly calcium carbonate. 

Magnesium. — Magnesium is also one of the elements essential 
for plant growth. It is found throughout the plant in smaller amounts 
than calcium, but is more abundant than the latter in the seeds and 
seems to aid in seed formation. In the animal body, magnesium 
usually accompanies calcium, but in much smaller amounts. 

Iron. — A small amount of iron is required by the higher plants 
for the formation of the green coloring matter (chlorophyl) by means 
of which they assimilate the carbon dioxid of the air. In the ani- 
mal, iron in small quantity is necessary for the formation of the red 
coloring matter (haemoglobin) of the blood which is the agent for 
conveying the oxygen of the air to the tissues. While, therefore, but 
a very small amount of iron is required by either plants or animals, 1 
it is nevertheless essential to the most fundamental processes of life. 

1 It is estimated that the blood of an adult man contains about 3 grams of iron. 



THE COMPONENTS OF PLANTS AND ANIMALS 7 

Phosphorus. — Phosphorus is another of the elements essential to 
plant growth, its chief function seeming to be to aid in the produc- 
tion and transportation of the proteins. It is found in all parts of 
the plant but accumulates especially in the seeds. 

Plants may contain more or less phosphorus in the form of phos- 
phates, especially in their vegetative organs. Even in the latter, 
however, a considerable share of it is in " organic" combination, while 
in the seeds but very small amounts of "inorganic" phosphorus are 
found. The "organic" phosphorus of plants is contained chiefly in 
three classes of compounds, viz., the phosphatids (37, 38), or so- 
called phosphorized fats, the nucleo- and phospho-proteins (52, 55), 
and phytin, the latter being the chief phosphorus compound of seeds. 
Phytin is a compound of phosphoric acid and inosit and may be split 
up into these constituents by hydrolysis and also by an enzym found 
in seeds. 

In the animal, the great store of phosphorus is found in the skele- 
ton, where it exists, as already stated, chiefly in the form of calcium 
phosphate. It is also found somewhat abundantly in the soft tissues 
of the body, of which it is an essential ingredient. Here it seems to 
exist largely in "organic" combination in the phosphatids and the 
nucleo- and phospho-proteins. 

Sulphur. — Sulphur is taken up by the roots of the plant in the 
form of sulphates, and when plant or animal substances are burned, 
more or less of the sulphur which they contain is found as sulphates 
in the ash. For these reasons, sulphur has been commonly regarded 
as one of the ash ingredients of plants and animals. As a matter of 
fact, however, as already pointed out, it is usually as truly an "or- 
ganic" ingredient as nitrogen or carbon. In particular, it is one of 
the elements of which the proteins are composed, and seems to exist 
in the plant and animal chiefly in this form. 

Chlorin. — Chlorin is found in plants associated with sodium. 
It does not seem to be necessary to plant life. In the animal it is an 
essential element in the gastric juice. 

Small amounts of fluorine and traces of iodin and of manganese 
and other catalysts also occur, but their specific functions are obscure 
except that fluorin is an ingredient of the enamel of the teeth. 



§ 2. The Carbohydrates 

6. Occurrence. — Although substances belonging to this 
group of compounds are found in the bodies of animals, they 
are especially characteristic of plants. Starch, one of the most 
familiar of them, is the first visible product of the assimilation 



8 NUTRITION OF FARM ANIMALS 

of carbon dioxid by chlorophyl-b earing plants, and the great 
mass of vegetable tissue is composed either of carbohydrates or 
of their nearly related derivatives. 

The more common carbohydrates have been known for a long 
time. Starch is familiar to us in the mealy portion of grains and 
in certain tubers, and cellulose in cotton and linen and, in im- 
pure forms, in the woody fiber of plants. Of the sugars, cane 
sugar has been known since almost prehistoric times, while the 
presence of this and other sugars in plant juices, in sweet fruits, 
honey, etc., is a familiar fact. The more common sugars were 
separated and identified quite early in the history of chemistry. 

7. Classification. — The carbohydrates contain hydrogen 
and oxygen in exactly the proportions to form water, and their 
name is derived from this fact, although compounds exist 
which contain two atoms of hydrogen to one of oxygen and 
yet are not carbohydrates, such, for example, as acetic acid, 
C2H4O2. The simplest of the carbohydrates are the simple 
sugars, more exactly designated as the monosaccharids. By 
polymerization, with elimination of water, the monosaccharids 
yield more complex carbohydrates which are conveniently classi- 
fied as di-, tri-, and polysaccharids. 

Monosaccharids, or simple sugars 

8. Composition. — The monosaccharids may be represented 
by the general formula C n H 2 „ O n . Substances having this gen- 
eral formula are known whose molecules contain from one to 
nine carbon atoms and which, from a chemical point of view, 
may be called carbohydrates. The simplest of these is formal- 
dehyde, CH 2 0, which is believed by many to be the first step in 
the synthesis of carbohydrates by the green plant. Only the 
C6 and C5 compounds, however, known respectively as the 
hexose and pentose carbohydrates, are of importance in their 
relations to nutrition. 

9. Hexoses. — The most important hexose monosaccharids 
are dextrose, levulose, galactose and mannose. 

Dextrose, ^-glucose, or grape sugar, is generally regarded as 
an aldose of the hexatomic alcohol sorbite. 

Sorbite : CH 2 OH- (CH ■ OH) 4 - CH 2 OH 
Dextrose : CH 2 OH- (CH • OH) 4 - CHO 



THE COMPONENTS OF PLANTS AND ANIMALS 9 

It occurs almost universally in the juices of plants along with 
levulose and cane sugar, and is found also in small amounts in 
the blood of mammals. Sixteen isomers of this compound 
are possible, twelve of which are known. 

Galactose and mannose are isomers of dextrose, occurring in 
nature only in combination as di- or polysaccharids. 

Levulose, or fruit sugar, is a ketose of sorbite, having the 
formula CH 2 OH- (CH • OH) 3 -CO-CH 2 OH, eight isomers 
being theoretically possible. It occurs mixed with dextrose in 
plant juices and in honey. 

The hexose monosaccharids are all soluble in water and 
readily diffusible and have a more or less sweet taste. All 
those found in nature are optically active, rotating the plane 
of polarized light. Thus dextrose, as its name implies, has a 
right-handed rotation and levulose a left-handed rotation. 
They reduce an alkaline solution of metallic salts, especially of 
copper, and this fact is utilized both as a qualitative test for 
them and as a means of quantitative determination. They are 
fermented by yeast, yielding as the chief products ethyl alcohol 
and carbon dioxid. 

10. Pentoses. — The pentoses are simple sugars, correspond- 
ing to the hexoses but having the general formula C5H10O5. 
Those occurring in nature are aldoses. Like the hexoses, they 
reduce metallic oxids, but unlike them they are not ferment- 
able by yeast. 

Arabinose. — By the hydrolysis of gum-arabic or cherry gum, 
there is produced dextro-rotatory arabinose (/-arabinose). Levo- 
rotatory arabinose (d-arabinose) has been prepared artificially. The 
inactive or racemic form (i-arabinose) has been found in human 
urine in small amounts. 

Xylose. — By the hydrolysis of wood gum there is produced a 
dextro-rotatory pentose known as /-xylose. The levo-rotatory form 
of the same sugar (J-xylose) is obtained in the hydrolysis of certain 
nucleo-proteins, the pentose group seeming to be a constituent of 
the molecule of those compounds. 

Rhamnose is a derivative of the pentose sugars in which an atom 
of hydrogen has been replaced by methyl. It occurs somewhat 
widely in the vegetable kingdom. 



IO NUTRITION OF FARM ANIMALS 

Glucosids 

11. The monosaccharids not only occur in the free state but 
also in combination with a great variety of substances in the 
so-called glucosids. The glucosids readily undergo hydrolytic 
cleavage into their two (or more) constituents, either by the 
action of chemical reagents or of enzyms. For example, the 
amygdalin of the bitter almond yields two molecules of dextrose, 
one of benzaldehyd and one of hydrocyanic acid, and cerebron, 
a constituent of the brain, splits up into cerebronic acid, sphin- 
gosin and galactose. Among other more or less familiar glucosids 
may be mentioned salicin, saponin, phloridzin and digitalin. 

Disaccharids 

12. The hexose group. — The disaccharids may be regarded 
as polymers or anhydrids of the monosaccharids, formed by the 
union of two molecules of the latter with the elimination of one 
molecule of water. The only disaccharids at present known be- 
long to the hexose group and their formation may be repre- 
sented by the equation CeHi 2 06 + CeHi 2 06 = C12H22O11 + H 2 0. 
From another point of view they are termed by some writers 
glucosids of the monosaccharids. 

Sucrose. — Sucrose, or cane sugar, has probably been longest 
known of the more familiar carbohydrates. It is found in the 
juices of the sugar cane and sorghum, in the sugar beet and in 
the sap of the maple, all of which are utilized as commercial 
sources of sugar. In smaller amounts it is present in a large 
number of plants. 

By the action of heat, aided by a dilute acid or alkali, or by 
the action of certain enzyms, notably the invertase of yeast, 
the reverse of the general reaction for the formation of the 
disaccharids may be brought about, one molecule of sucrose 
combining with one molecule of water to yield one molecule 
each of dextrose and levulose. 

C12H22O11 + H2O = C6H12O6 -f- C6H12O6 

Sucrose rotates the plane of polarized light to the right, 
while, owing to the fact that the rotatory power of levulose is 
greater than that of dextrose, the mixture of equal parts of the 
two which is formed in the foregoing reaction rotates to the 



THE COMPONENTS OF PLANTS AND ANIMALS II 

left. On account of this fact, this breaking up of cane sugar 
has been called inversion and the use of this term has been 
extended to designate in general the hydrolytic cleavage of di- 
saccharids into their constituent monosaccharids. 

Lactose. — Lactose, or milk sugar, is a characteristic ingredi- 
ent of the milk of mammals. Like sucrose, it may be broken 
up, with the addition of one molecule of water, into two mole- 
cules of monosaccharids, in this case dextrose and galactose. 
It is less soluble than sucrose and therefore less sweet to the 
taste, having a gritty feel in the mouth. It is not found in 
plants. 

Maltose. — By the action of certain ferments upon starch 
during the germination of seeds and also in the digestive tract 
of animals, a disaccharid known as maltose is produced. It is 
therefore present abundantly in malt, whence its name. This 
sugar when hydrolyzed yields two molecules of dextrose. 

13. General properties. — The disaccharids are crystalline, 
soluble in water and optically active. Sucrose does not reduce 
an alkaline copper solution, but lactose and maltose do. The 
disaccharids are not fermentable. Any cases in which they are 
apparently fermented are found to be preceded by some action 
which inverts or breaks up the disaccharids into their con- 
stituent monosaccharids. 

Trisaccharids 

14. By the union of three molecules of C6Hi 2 6 with the 
elimination of two molecules of water, there may be formed 
the compound Ci 8 H 3 20i 6 , called a trisaccharid. One such, 
known as ramnose, is present in the sugar beet, the cotton seed, 
in barley and in wheat. Upon hydrolysis it yields one mole- 
cule each of dextrose, levulose and galactose. 

Polysaccharids 

15. Chemical structure. — The polysaccharids, like the di- 
saccharids, are anhydrids, but are formed by the combination of 
many molecules of the monosaccharids and have a correspond- 
ingly high molecular weight. The general formula of the hexose 
polysaccharids is (C 6 H 10 O5) n , the value of n doubtless varying 



12 NUTRITION OF FARM ANIMALS 

through a wide range, but the molecular weights of the in- 
dividual polysaccharids have not been finally determined. 

The polysaccharids are tasteless and usually amorphous sub- 
stances which, with the exception of cellulose, are more or less 
soluble in water. They are optically active but in general are 
not diffusible through membranes. They are hydrolyzed easily, 
especially by the action of heat and acids and by enzyms, yield- 
ing ultimately monosaccharids. 

In addition to their common names, they are designated by 
terms derived from the monosaccharids out of which they are 
built up. Thus starch, which is an anhydrid of dextrose and 
yields only this sugar upon hydrolysis, is a dextran. Similarly, 
there are levulans, galactans, mannans, arabans, xylans, etc., 
yielding the corresponding sugars when hydrolyzed. In the 
same manner, it is customary to distinguish between the 
hexosans, derived from the hexoses, and the pentosans, the 
anhydrids of the pentoses. 

16. The hexosans. — This group of carbohydrates includes 
those which are most abundant in the vegetable kingdom and 
of the greatest significance as sources of nutriment for man and 
animals, viz., starch, the dextrins and gums, and cellulose and 
its various derivatives. It will be convenient to consider the 
more important hexosans somewhat in the order of their re- 
sistance to solvents. 

17. Cellulose. — Cellulose constitutes the basis of the cell 
walls of plants and is also found in certain lower animals (tuni- 
cates). Clean cotton consists of nearly pure cellulose, each 
fiber being a single cell from which the contents (protoplasm) 
have nearly disappeared. Linen and the best qualities of paper 
are other examples of nearly pure cellulose. A crystalline 
form has also been described. 

Cellulose is insoluble in water and comparatively resistant 
to reagents in general. Plants, however, contain enzyms 
(cytases) which are able to bring it into solution in the processes 
of plant growth, and apparently these enzyms play some part 
in its digestion by animals. It is also attacked and dissolved 
by some species of bacteria. Concentrated sulphuric acid dis- 
solves it, and the solution, on dilution and boiling, undergoes 
hydrolysis, yielding dextrose. Cellulose is therefore a dextran. 
Its molecular weight is unknown. 



THE COMPONENTS OF PLANTS AND ANIMALS 13 

18. Hemicelluloses. — These polysaccharids differ from true 
cellulose in being hydrolyzed by comparatively short boiling 
with dilute acids and further in the fact that the hydrolysis, 
instead of yielding only dextrose, as in the case of cellulose, 
produces a variety of both hexose and pentose sugars, the 
former including galactose, mannose and levulose, as well as 
dextrose, and the latter arabinose and xylose. The hemicellu- 
loses must be regarded, therefore, as containing both hexosans 
and pentosans, but whether in mixture or chemical union is 
uncertain. While true cellulose constitutes the framework of 
the plant, the hemicelluloses serve to a greater or less extent as 
reserve material. In the conventional method of feeding stuffs 
analysis, the hemicelluloses are found both in the " crude fiber " 
(109) and in the " nitrogen-free extract " (110). 

19. Lignin. — In the young plant, the cell walls consist of 
nearly pure cellulose. With advancing maturity they become 
thickened, not only by the formation of additional cellulose and 
of hemicelluloses but by the deposition of numerous " incrusting 
substances," the most important group of which has received 
the collective name of lignin. These substances contain a con- 
siderably higher percentage of carbon than cellulose (54 to 60 
per cent) and may be separated from the latter by oxidizing 
agents. The substances of the lignin group contain methoxyl 
(— O • CH 3 ) and ethoxyl (— O • C 2 H 5 ) groups in considerable 
amount, and by some are regarded as substituted celluloses. 

20. Crude fiber. — The so-called "crude fiber" (109) of 
plants contains most of the cellulose and lignin of the cell walls 
and in addition a third group — the cutin group 1 — whose per- 
centage of carbon is still higher (60-75 P er cent). Cutin appears 
to be indigestible. 

21. Starch. — Starch is one of the most common and impor- 
tant of the vegetable carbohydrates. In the growth of plants, 
starch is formed in the green leaves by the aid of light, and is 
the first visible product of assimilation. In the mature plant, 
it is stored up in large quantities in the seed or in the tuber to 
supply the needs of the new plant. Hence the common grains, 
corn, wheat, oats, barley, etc., as well as potatoes, are rich in 
starch and form commercial sources of it. The seeds of most 
legumes contain it in less amounts but still abundantly. In 

1 Compare Konig: Landw. Vers. Stat., 65 (1907), 55. 



14 NUTRITION OF FARM ANIMALS 

the oil seeds it is replaced by oil. It is not found in the animal 
body. 

Starch occurs in plants in the form of microscopic granules, 
which have a peculiar form for each species, so that we may speak 
of the starches rather than of starch. These grains consist of 
a surrounding envelope consisting of a variety of cellulose in- 
closing a more soluble substance or substances known as granu- 
lose. When treated with much hot water the starch grain swells 
and bursts the envelope and the enclosed granulose dissolves, 
probably after undergoing more or less hydration. 

Starch may be hydrolyzed readily by dilute acids or alkalies 
or by heat. The final product of its hydrolysis is dextrose, 
which in an impure form constitutes commercial glucose or 
starch sugar. Starch is therefore a dextran. As already noted, 
certain enzyms, notably those formed in germinating seeds 
and others secreted in the digestive tract of animals, act upon 
starch readily with the production of maltose. Starch is also 
acted upon by some species of bacteria with the formation of 
lactic, butyric and other acids, methan and in some cases hy- 
drogen. 

22. Galactans. — Galactans occur more particularly in le- 
guminous plants, other feeding stuffs being comparatively free 
from them. 

23. Inulin. — The roots of the artichoke, dahlia, dandelion, 
chicory and other composite contain instead of starch a quite 
similar carbohydrate, inulin, which on hydrolysis yields levulose 
instead of dextrose, i.e., it is a levulan. 

24. The dextrins. — In the hydrolysis of starch a series of 
ill-defined, intermediate compounds is produced, collectively 
called dextrins. Commercial dextrin is made by heating moist 
starch to about 235 Fahrenheit. It is likewise produced in the 
cooking of starchy materials, the brown crust of bread, for 
example, consisting largely of dextrin. Various dextrins have 
been separated and described, but it seems questionable 
whether the investigators have worked with definite chemical 
individuals. For the present, it seems wiser to speak collec- 
tively of the dextrins as intermediate products between starch 
and the simpler di- and mono-saccharids. 

25. Glycogen. — In the liver and muscles of animals, and to 
a less degree in other parts of the body, there is found in rather 



THE COMPONENTS OF PLANTS AND ANIMALS 15 

small amounts a carbohydrate called glycogen. Glycogen has 
the same percentage composition as starch and has sometimes 
been called animal starch, although improperly, since its proper- 
ties are quite different from those of starch. It has important 
functions in the animal, as will appear later. It is not found in 
the plant. It is readily soluble in water, yielding an opalescent 
solution. The empirical formula of glycogen is the same as 
that of starch. When hydrolyzed it yields only dextrose, and 
is therefore a dextran. 

26. The gums. — Familiar examples of this class of sub- 
stances are gum arabic and the gums of the cherry, peach and 
plum. The mucilage of flax seed closely resembles the gums, 
and other seeds also contain gum-like bodies. Upon hydrolysis, 
the gums yield hexoses, especially galactose, showing that they 
contain galactans. In addition to hexoses, however, they yield 
sugars belonging to the pentose group. 

27. The pentosans. — The pentosans may be regarded as 
polymers or anhydrids of the pentoses, corresponding in this 
respect to the polysaccharids of the hexose group. Their 
general formula is (C 5 H 8 04) n , but their molecular structure is 
unknown. 

Araban. — This is a constituent of gum arabic and other 
gums, as shown by the fact that these gums, as already noted 
(10), yield /-arabinose when hydrolyzed. 

Xylan. — This compound is also known as wood gum. It 
can be extracted from various woods, from the cob of maize 
and from various other vegetable materials by the action of 
dilute alkalies, and yields /-xylose when hydrolyzed. In the 
plant, araban and xylan appear to be in a more or less close 
chemical combination with hexosans, especially in the cell walls 
of the more mature plant, constituting the so-called tfemi- 
celluloses (18). 

Pectins. — Most ripe fruits, as well as the flesh of beets, 
turnips and similar roots, contain a group of substances called 
the pectin group. As they exist in the roots or fruits they are 
insoluble in water, but by cooking they are converted into sub- 
stances which form the basis of fruit jellies. On hydrolysis 
they yield pentoses, chiefly arabinose. 



1 6 NUTRITION OF FARM ANIMALS 

§ 3. Fats and Related Bodies — the Lipoids 

28. Classification. — Under the rather vague term " lipoids," 
or fat-like substances, there are included, besides true fats, a 
large number of chemical individuals of varied and complex 
molecular structure. Chemically, these substances (with the 
exception of the cholesterins) are characterized by containing 
radicles of the so-called fatty acids, principally the higher ones 
of the series. Physically, the lipoids have been defined, prin- 
cipally from the standpoint of the physiological chemist, as 
substances which are soluble in organic solvents, such as ether, 
alcohol, chloroform or benzol. This latter definition, however, 
includes substances, such as the cholesterins, which would be 
excluded by the chemical definition just given. For the present 
purpose, the principal lipoids may be conveniently grouped under 
five heads : (1) fats, (2) waxes, (3) cholesterins, (4) phosphatids 
or phospholipins, (5) cerebrosids or galactolipins. 

The Fats 

29. Occurrence. — It is a familiar fact that the bodies of 
animals contain a not inconsiderable amount of fat, the per- 
centage seldom falling below six in the very lean animal while it 
may rise as high as forty in the very fat animal. The fat is 
the reserve material of the body and is contained in what is 
called adipose tissue (94) , consisting of cells of connective tissue 
more or less filled with fat. Larger or smaller amounts of adi- 
pose tissue are found in all parts of the body but especially in 
the subcutaneous tissues, the tissues surrounding the intestines, 
and, particularly in fat animals, in the muscles. 

In plants, fats are usually less abundant. They occur in 
all parts of the plant but are especially stored up in the seeds, 
where they serve as reserve material which is metabolized 
during germination. Some seeds, like those of cotton, flax 
and rape, contain fat so abundantly that they are commercial 
sources of oil. In the plant,' the fat is not deposited in special 
tissues but is usually distributed through the protoplasm of 
the cell. Both animal and vegetable fats are mixtures of 
various simple fats, often containing also small amounts of 
free fatty acids. 



THE COMPONENTS OF PLANTS AND ANIMALS 17 

30. Molecular structure. — The simple neutral fats are tri- 
glycerids, that is, they are esters of the triatomic alcohol 
glycerol with monobasic fatty acids, the hydrogen atoms of 
the three hydroxy Is being replaced by the acid radicles. Their 
general formula is as follows, Ri, R 2 and R 3 representing the 
acid radicles, which may or may not be the same : — 

Glycerol CH 2 . OH — CH • OH — CH 2 . OH 
Neutral fat CH 2 - ORi — CH . OR 2 — CH 2 . OR 3 

The fatty acids may be divided into the saturated and the 
unsaturated. The saturated fatty acids have the general for- 
mula C n H 2n 02 and are the normal acids of the aliphatic series, 
the two lower members of which are familiar as formic and 
acetic acids. The general formula of these acids is as follows, 
each carbon atom being united to the adjacent ones by a single 
bond. 

CH 3 -(CH 2 ) n -COOH 

The two principal saturated acids contained in the animal fats 
are stearic acid, C18H36O2, and palmitic acid, C16H32O2. Besides 
these two, however, others are also found in small amounts. 
In butter fat, especially, several of the lower acids of the series 
are present, the principal ones being butyric, C4H8O2, caproic, 
C 6 Hi 2 2 , caprylic, C 8 Hi 6 2 , capric, C10H20O2, lauric, C12H24O2 
and myristic, C14H28O2. In the body fats there have been 
found also higher acids of the same series, particularly arachnic 
acid, C20H40O2. 

The unsaturated fatty acids differ from the saturated acids 
in containing two or more carbon atoms united by two bonds 
instead of one and consequently in containing less hydrogen 
than the saturated acids. Of the unsaturated acids, the most 
abundant in animal fats is oleic acid, having the formula 

CH 3 -(CH 2 ) 7 -CH = CH-(CH 2 ) 7 -COOH 

The eruic acid of rape oil also belongs to this series, and the 
linoleic acid, C18H32O2, of linseed oil and other drying oils belongs 
to a related series of unsaturated acids of the general formula 
C n H 2n _402 with two double unions of carbon atoms. 

It is a noteworthy fact that nearly all the fatty acids occurring 
in the animal body contain an even number of carbon atoms, 
c 



1 8 NUTRITION OF FARM ANIMALS 

31. Chemical reactions. — Of the chemical reactions of the 
fats, the one of most importance physiologically is that known 
as saponification, or more strictly as hydrolysis. It consists of 
a cleavage and hydration of the molecule, yielding glycerol and 
fatty acids. The most familiar instance of this reaction is in 
the process of soap making. For example, if tri-stearin is acted 
upon by potassium hydrate the final result is as represented 
by the following equation : — 

C 3 H5(C 18 H 3 50 2 )3 + (KOH) 3 = (KC 18 H 3 50 2 ) 3 + C 3 H 8 3 

Tristearin Potassium hydrate Potassium tristearate Glycerol 

In this reaction, the alkali salt of the fatty acid, that is, a 
soap, is obtained. By the action of water at temperatures con- 
siderably above ioo° C, essentially the same result is reached 
except that the free acid is obtained instead of the salt. The 
same decomposition may also be effected by means of acids, 
which probably act as catalyzers. 

Of most importance physiologically is the hydrolysis of fat by 
means of enzyms. Such enzyms are produced by certain plants 
and are also found in various digestive juices, notably in the 
secretion of the pancreas. These enzyms have received the 
general name of lipases. The hydrolysis of fats by enzyms 
appears to be a reversible reaction, at least with the glycerids 
of low molecular weight. In other words, the same enzym 
may effect the cleavage of a glycerid or the combination of 
glycerol and the fatty acid, the reaction in either case reaching 
an equilibrium at a certain stage. 

32. Physical properties. — Certain general properties are 
common to all the fats. Their specific gravity is in all cases 
less than one, so that they float on water. They have a fatty 
feel and leave a permanent grease spot on paper or fabric. They 
are almost insoluble in water, although water is soluble to a not 
inconsiderable extent in fats. They are readily soluble in ether, 
benzol, carbon disulphid and most of them in petroleum ether, 
but only sparingly in alcohol. 

The melting point of the fatty acids increases with the 
molecular weight. The exact melting point of a fat is diffi- 
cult to determine, but for the three common glycerids and 
the corresponding acids it may be stated approximately as 
follows : — 



THE COMPONENTS OF PLANTS AND ANIMALS 19 

Melting Points 

Olein . . -4 to -5 C. 

Oleic acid 14 C. 

Palmitin 63 to 65 C. 

Palmitic acid 62. 6° C. 

Stearin 71.6 C. 

Stearic acid 71.5 C. 

A distinction is commonly made between fats and oils, the 
fats being solid at ordinary temperatures and the oils liquid. 
The difference depends largely upon the proportion in which 
the various simple fats are present. Olein and other fats con- 
taining unsaturated acids are usually liquid at room temper- 
ature and their presence increases the softness of the fat. 

The fatty acids of higher molecular weight are volatile only 
at comparatively high temperatures and at reduced pressure. 
Those of lower molecular weight, notably those contained in but- 
ter fat, can be readily distilled in a current of steam and their 
proportion serves to distinguish butter fat from other animal 
fats. 

An important physical property of the fats, which, however, 
is by no means peculiar to them, is that of forming what is 
known as an emulsion. Fat is said to be emulsified when, in 
the liquid state, it is distributed in minute droplets or globules 
throughout some other liquid ; for example, if fat be violently 
shaken with water an emulsion is formed. Such an emulsion 
is not permanent, however, the fat droplets very soon coalescing 
and rising to the surface. The presence of small amounts of 
certain other substances dissolved in the water, however, will 
prevent this separation and give rise to a permanent emulsion. 
The most common substance producing this effect is soap. 

Certain gums and also proteins likewise serve to retain fat 
in the emulsified state. The most familiar example of such an 
emulsion is milk, the fat being held in suspension in this case 
by the action of the proteins of the milk. This effect of various 
substances in retaining fat in the emulsified form depends upon 
their effect upon the surface tension of the contact layer be- 
tween fat and water, but a full discussion of this point would 
be out of place in this connection. 

33. Native fats. — As has already been stated, the reserve 
fats of the animal body are triglycerids, chiefly of stearic, oleic 



20 



NUTRITION OF FARM ANIMALS 



and palmitic acids, although small quantities of esters of lauric, 
myristic and arachnic acids and frequently free fatty acids are 
also found, as well as minute amounts of esters of the higher 
alcohols, coloring matter, etc. Since stearin and palmitin are 
solid at ordinary temperatures, while olein is liquid, the con- 
sistency of a fat depends largely upon the proportion of olein 
which it contains and varies not only between different species 
of animals but often in different parts of the body of the same 
animal. The fats of cold-blooded animals contain more olein 
than those of warm-blooded animals and therefore remain liquid 
at lower temperatures. 

The vegetable fats contain a greater variety of fatty acids 
than the animal fats, notably unsaturated acids like linoleic 
and eruic, as well as oxy-acids and esters of the higher alcohols 
(waxes), while the so-called crude fat, or ether extract (108) of 
vegetable materials contains a great variety of ether-soluble 
substances, including waxes, resins, chlorophyl, etc., some of 
which are but remotely related to the true fats. 

34. Elementary composition. — The three principal triglyc- 
erids, stearin, palmitin and olein, while differing in formula 
and molecular weight, differ but little in their elementary com- 
position, as the following table shows : — 

Table i. — Composition of Triglycerids 



Carbon 

Hydrogen 

Oxygen 

Total 



Tristearin 

% 


Tripalmitin 

% 


76.77 

12.45 
10.78 

100.00 


75-86 
12.24 
11.90 

LOO.OO 



Triolein 
% 



77-31 
11.84 

10.85 

100.00 



Naturally, therefore, the composition of the ordinary mixed 
animal fats varies but little, either in different individuals or in 
different species of animals. The classic investigations of 
Schulze and Reinecke 1 upon the composition of animal fats 
gave the following results. 



1 Landw. Vers. Stat., 9 (1867), 97- 



THE COMPONENTS OF PLANTS AND ANIMALS 21 
Table 2. — Composition of Animal Fats 





No. OF 
Samples 


Carbon 


Hydrogen 


Oxygen 




Aver- 
age 
% 


Maxi- 
mum 
% 


Mini- 
mum 
% 


Aver- 
age 
% 


Maxi- 
mum 

% 


Mini- 
mum 
% 


Aver- 
age 

% 


Maxi- 
mum 
% 


Mini- 
mum 
% 


Beef fat • . 
Pork fat . . 
Mutton fat . 


10 

6 

12 

28 


76.50 

76.54 
76.61 

76.50 

76.63 
76.56 
76.07 
77.62 


76.74 
76.78 
76.85 


76.27 
76.29 
76.27 


n. 91 
H-95 

12.03 

12.00 

12.05 
11.90 
11.69 
11.94 


12. 11 

12.07 
12.16 


11.76 
11.86 
11.87 


n-59 
11.52 
11.36 
11.50 

n.32 

11.44 
11.24 

11.44 


11.86 
n.83 
11.56 


11. 15 
11. 15 
11.00 


Average 

Dog . . . . 

Cat ... . 
Horse . . . 
Man . . . 







Benedict and Osterberg 1 obtained the following for the com- 
position of human fat : — 

Table 3. — Composition of Human Fat 





Carbon 


Hydrogen 




% 


% 


Sample No. 1 


76.29 


11.80 


Sample No. 2 






















76.36 


11.72 


Sample No. 3 






















75.85 


11.87 


Sample No. 4 






















75-95 


n.85 


Sample No. 5 






















75-94 


11.74 


Sample No. 6 






















76.07 


11.69 


Sample No. 7 






















76.13 


11.84 


Sample No. 8 






















76.05 


11. 81 


Average 






• 
















76.08 


11.78 



The average carbon content of animal fat is commonly con- 
sidered to be 76.5 per cent. 

Waxes 

35. In popular usage, the distinction between fats and waxes is 
based upon their obvious physical properties, substances having the 
well-known greasy feel being called fats or oils according to their 
consistency at ordinary temperatures while the waxes are solid, can 
be kneaded and lack largely or wholly the greasy feel. 

1 Amer. Jour. Physiol., 4 (1901), 69. 



2 2 NUTRITION OF FARM ANIMALS 

Chemically, waxes are defined as fatty acid esters of alcohols other 
than glycerol, while the fats have already been defined as the fatty 
esters of glycerol. This distinction is far from according with com- 
mon usage. Under it many substances popularly known as waxes 
are technically fats, as for example, Japan wax and in part beeswax. 
On the other hand, numerous materials ordinarily regarded as oils or 
fats must be designated as waxes. One of the most familiar bodies 
of this class is spermaceti, commonly regarded as a fat, which consists 
chiefly of the palmitic ester of cetyl alcohol, CH3(CH 2 )i4CH 2 OH, and 
sperm oil, which contains no glycerids, would also be regarded as a 
liquid wax. Similarly wool fat is chemically a mixture of waxes, in- 
cluding the stearic esters of cholesterin and isocholesterin. Beeswax 
is likewise in part a true wax, containing the palmitic ester of myricyl 
alcohol, CH3(CH 2 )28CH 2 OH. The secretion of the anal glands of 
certain birds contains esters of octodeckyl alcohol, C18H37OH. 

Cholesterins 

36. Substances of this group are found in the nonsaponifiable resi- 
due of various fats. In the animal organism they are found widely 
distributed through the tissues in small amounts and are appar- 
ently normal constituents of protoplasm. As just noted, they are 
especially abundant in wool fats in combination with stearic acid. 
They are also widely distributed in plants. Their exact constitution 
is still unknown, but they contain a single alcohol hydroxyl and ap- 
parently belong to the terpene group. Their formula is C27H44OH, 
or C 2 7H460H, more probably the latter. From the chemical point 
of view, they are entirely unrelated to the other groups classified as 
lipoids, but biologically their functions appear to be closely related 
to those of the other ether-soluble cell constituents. 

Phosphatids or Phospholipins 

37. Lecithins. — Quite closely related to the fats are the 
substances known as lecithins, which are sometimes, although 
inexactly, called phosphorized fats. Like the fats, the leci- 
thins are esters of glycerol. They differ from the fats in that 
only two of the hydroxyls of the glycerol are replaced by fatty 
acid radicles, the third being replaced by phosphoric acid 
which is also in combination with the nitrogenous base cholin, 
a derivative of glycol. The lecithins, therefore, contain, in 
addition to carbon, hydrogen and oxygen, both phosphorus and 
nitrogen. 



THE COMPONENTS OF PLANTS AND ANIMALS 23 

The molecular structure of the lecithins is illustrated by the fol- 
lowing formula for distearyl lecithin : — 

CH 2 -0-Ci 8 H 36 

CH -0-C 18 H 35 

I 
CH 2 -0 

\ 

HO-PO 

/ 
CH 2 -0 

CH 2 -N - (CH 3 ) 3 
OH 

The lecithins resemble fats in their general properties. They 
are soluble in ether but, unlike the fats, readily form permanent 
emulsions or colloidal solutions with water. On hydrolysis, 
they yield fatty acids, glycero-phosphoric acid and cholin. 
They are found widely distributed both in animals and plants 
and appear to be essential constituents of protoplasm. 

38. Other phosphatids. — A variety of other lipoids of the type of 
the lecithins, but differing in both the fatty acid and the nitrogenous 
base which they contain and likewise in the ratio of phosphorus to 
nitrogen, have been described, but the chemistry of this group is still 
in a very unsatisfactory state. The various phosphatid preparations 
obtained from vegetable materials, especially seeds, by E. Schulze 
and his associates and designated as lecithins are held by other 
authors to be such only in a generic sense and in some cases are re- 
garded as more analogous to the cerebrosids or galactolipins of the 
succeeding paragraph. 

Cerebrosids or Galactolipins 

39. This group of substances, found especially in the brain and in 
nerve tissue in general, belongs chemically to the lipoids, since its 
members yield fatty acids on hydrolysis. The other products of 
hydrolysis are galactose and nitrogenous substances but no phosphoric 
acid, but the constitution of these compounds is still unknown. 



24 NUTRITION OF FARM ANIMALS 

§ 4. The Proteins 

40. Importance. — By far the larger share of the organic 
matter of the animal body, aside from fat, consists of sub- 
stances belonging to the well-defined group of the proteins, 
these compounds, according to the results of analyses recorded 
on subsequent pages (98), making up from 17.5 to 21 per cent 
of the fat-free body. These substances are characteristic of 
the animal body, as the carbohydrates are of plants. Biologi- 
cally, they are of prime importance to both plants and animals, 
since they form the basis of the cytoplasm and nucleus of 
every living cell. 

41. Nomenclature. — The chemical structure of the pro- 
tein molecule has until quite recently been almost entirely un- 
known and even yet has been but very partially unraveled. 
Accordingly, the basis for a scientific classification of these 
substances has been lacking. As a matter of necessity, there- 
fore, the nomenclature hitherto followed has been based chiefly 
on their physical properties, more particularly their solubilities 
and coagulation temperatures. Naturally, such a classification 
has been far from satisfactory and this has been the more true 
on account of the difficulty of accurately separating the differ- 
ent proteins either by precipitation or crystallization. 

Accordingly, there has existed a great and confusing diversity 
in the nomenclature of the proteins, and uniformity is still far 
from having been reached. For the present, it seems desirable 
to follow the classification and nomenclature which has been 
adopted provisionally by the American Physiological Society 1 
and the American Society of Biological Chemists. 2 This 
nomenclature rejects entirely the term proteid as ambiguous 
on account of the wide diversity in its use, and employs protein 
as a general term to signify the group of substances which, 
according to the nomenclature adopted by the Association of 
American Agricultural Colleges and Experiment Stations in 
1898, 3 was called proteids. In other words, protein under the 
new plan excludes altogether the non-protein nitrogenous 
substances of plants and animals. 

1 Proceedings, Amer. Physiol. Soc, Amer. Jour. Physiol., 21 (1908), xxvii. 

2 Proceedings, Amer. Soc. Biol. Chemists, 1, 142. 

3 U. S. Dept. Agr., Office of Expt. Stas., Bui. 65, pp. 11 7-123. 



THE COMPONENTS OF PLANTS AND ANIMALS 25 

The proteins in this sense are subdivided into : — 

1. Simple proteins 

2. Conjugated proteins 

3. Derived proteins 

Simple proteins are defined as those yielding only a 
amino acids or their derivatives upon hydrolysis. Conju- 
gated proteins are those which contain the protein mole- 
cule united to some other molecule or molecules otherwise than 
as a salt. Derived proteins are the products of the hydrolytic 
cleavage of the protein molecule and include a wide range of 
substances, from slightly altered protein to the peptids. 

42. Physical properties. — In the dry state, the proteins are 
in general white or slightly tinted substances. They are usually 
amorphous, but a number of them have also been obtained in 
the crystalline form and some are found crystallized in nature. 
Some of the proteins are soluble in water, others only in salt 
solutions or in acids or alkalies. They are insoluble in- most 
other ordinary solvents. 

The proteins belong to the class of colloids, i.e., they do not 
diffuse through membranes and are claimed to have no osmotic 
pressure when free from electrolytes. Colloids in general exist 
in two forms, a liquid form, technically known as a sol, and a 
solid form called a gel, the difference being well illustrated by 
the familiar substance gelatin. When a colloid is distributed 
through water so as to form an apparent solution the latter is 
known as a hydrosol. Whether the proteins are to be regarded 
as soluble in water, or whether their apparent solution is in 
reality a suspension, has been much discussed. It has been 
shown, however, that these solutions are conductors of electricity 
and it has been concluded that they are true solutions. It may 
be said, however, that no sharp boundary exists between a 
true solution and a suspension but that an indefinite number of 
intermediate stages is possible. As a matter of convenience, 
however, we may speak of solutions of the proteins. 

Different proteins may be precipitated from their solutions 
by various reagents, particularly acids, alkalies and metallic 
salts. Ammonium sulphate, especially, has been largely used 
for the purpose of separating different proteins by means of 
fractional precipitation. 



26 NUTRITION OF FARM ANIMALS 

f 

43. Coagulation. — An important property of the proteins 
is that of coagulation. For instance, if a solution of ordinary- 
egg albumin be heated to 55 C. the albumin begins to separate 
in an insoluble form and at about 6o° C. the precipitation is 
complete. This change differs from the change in the case of 
gelatin solutions from liquid to solid in being irreversible, i.e., 
coagulated protein cannot be changed back to the soluble form. 
It should be noted that this change is entirely distinct from the 
precipitation of proteins by means of ammonium sulphate for 
example. The exact nature of the change is unknown, but it 
would seem to be in part chemical in character. 

All forms of protein appear to be subject to coagulation in 
the chemical sense of the word. Thus the precipitated proteins 
obtained from solutions are at first in the colloidal form but on 
standing pass more or less rapidly into the coagulated or " de- 
natured " form. The same is true of the solid proteins like 
fibrin, etc. The coagulated proteins are insoluble in water 
and salt solutions, but may be dissolved in acids or alkalies. 

The simple proteins 

44. Composition. — The simple proteins differ from the com- 
pounds considered in the previous sections in containing, in 
addition to carbon, hydrogen and oxygen, the elements nitro- 
gen and sulphur. Notwithstanding the considerable variation 
in the properties of the different simple proteins and the notable 
differences which have been shown to exist in their chemical 
structure, their elementary composition differs but little. 
Cohnheim 1 quotes the following figures from Michel for the 
composition of serum albumin, which is in many respects a 
typical animal protein. 

Carbon 53-o8 

Hydrogen 7.10 

Nitrogen iS-93 

Sulphur 1.90 

Oxygen 21.99 

100.00 

The variations in the percentages of the principal elements 
as stated by Cohnheim * and by Plimmer 2 are : — 

1 Chemie der Eiweisskorper, 2d Ed., p. 151. 

2 The Chemical Constitution of the Proteins, Part I, p. 2. 



THE COMPONENTS OF PLANTS AND ANIMALS 



27 



Carbon 
Nitrogen . 
Hydrogen 



Sulphur 0.4 




Plimmer 



5i-55% 
15-17% 

7% 
0.4-2.5% 



As a rule, the vegetable proteins contain a higher percentage 
of nitrogen than do the animal proteins. 

45. Structure of the proteins. — The molecular structure of 
the proteins is very complex and their molecular weights are 
very large, but as yet no very satisfactory determinations of the 
latter magnitude have been made. Determinations of the 
molecular structure of haemoglobin (a conjugated protein) by 
two methods have given concordant results indicating a mini- 
mum molecular weight of 16,666, from which has been computed 
the formula C758Hi203Ni 96 FeS2. Confirmation of this result has 
been reported as the result of determinations of its osmotic 
pressure. 2 For the globin of haemoglobin, a minimum molecu- 
lar weight of between 5000 and 8000 has been obtained. For 
serum albumin, the figure 10,166 is reported, for egg albumin, 
5378, and for edestin 14,500. These figures are of value, how- 
ever, chiefly as showing the complex nature of the protein mole- 
cule. 

Up to within a comparatively few years, general statements 
like those just made marked the limits of our knowledge of the 
chemical nature of the proteins. The masterly researches of 
Emil Fischer, however, and especially his creation of new 
experimental methods, have resulted in a very great advance 
in knowledge, and to-day, thanks to his labors and those of a 
large number of investigators in applying and improving his 
methods, we possess a fairly definite general conception of the 
structure of the protein molecule. As in the investigation of 
chemical compounds in general, two lines of attack have been 
followed, viz., a study of the products resulting from the 
splitting up of the molecule and attempts to synthesize the 
compound from simpler substances of known composition and 
structure. 



1 Four to five per cent in keratins. 



2 Zentbl. Physiol., 21, 73°. 



28 NUTRITION OF FARM ANIMALS 

46. Hydrolysis of proteins. — The simple proteins readily 
undergo hydrolysis when acted upon by strong acids or alkalies, 
or by various enzyms such as the pepsin of the gastric juice, 
the trypsin of the pancreatic juice, etc. These various agents 
effect a succession of cleavages and hydrations resulting in a 
series of products of decreasing molecular complexity and in- 
creasing solubility, ranging from very slightly modified proteins 
through the so-called proteoses and peptones to still simpler 
substances. 

47. Cleavage products of proteins. — When the hydrolysis, 
especially acid hydrolysis, of the simple proteins is pushed as 
far as possible, there result a number of comparatively simple 
crystalline substances which are qualitatively the same for all 
proteins with a few exceptions, although the proportions of the 
various products obtained from different proteins vary ma- 
terially. It is believed, therefore, that the protein molecule is 
built up of these final products of hydrolysis, the so-called 
" building stones." 

These primary cleavage products of the simple proteins are 
all a amino acids. One of the first of them to be isolated was 
glycin or aminoacetic acid, represented by the following for- 
mula : — 

CH 3 CH 2 • NH 2 

I I 

COOH COOH 

Acetic acid Glycin 

The other cleavage products of the simple proteins may be 
regarded as derived from glycin by the replacement of one 
atom of hydrogen in the CH 2 group by various atomic group- 
ings. In all of them the NH 2 group occupies the same position 
in the molecule relative to the group COOH as in glycin, the 
so-called a position. The atomic grouping 

I 

CH • NH 2 

CO OH 

is therefore common to all of these bodies and determines their 
general chemical behavior as well as that of the proteins from 
which they are derived. 



THE COMPONENTS OF PLANTS AND ANIMALS 29 

The amino acids derived from the proteins may be divided 
into two classes ; the monamino acids, of which glycin is typi- 
cal, containing one NH 2 group, and the diamino acids, contain- 
ing two NH 2 groups. To these there are to be added certain 
heterocyclic compounds. Plimmer 1 gives the following list of 
the amino acids which have been identified with certainty among 
the cleavage products of the proteins. The presence of others 
has been claimed by several investigators. 

A. Monoaminomonocarboxylic acids 

1. Glycin, C2H5NO2, or aminoacetic acid. 

CH 2 ■ (NH 2 ) • COOH 

2. Alanin, C3H7NO2, or a-aminopropionic acid. 

CH 3 • CH(NH 2 ) • COOH 

3. Valin, C 5 HnN0 2 , or a-aminoisovalerianic acid. 

CH 3 \ 

CH ■ CH(NH 2 ) • COOH 
CH 3 / 

4. Leucin, C 6 Hi 3 N0 2 or a-aminoisocaproic acid. 

CH 3 \ 

CH • CH 2 • CH(NH 2 ) • COOH 
CH 3 / 

5. Isoleucin, C 6 Hi 3 N0 2 , or a-amino-|3-methyl-/3-ethyi-propionic acid. 

CH 3 v 

CH • CH(NH 2 ) • COOH 
C 2 H 5 / 

6. Phenylalanin, C 9 HnN0 2 , or jS-phenyl-a-aminopropionic acid. 

C 6 H 5 • CH 2 • CH(NH 2 ) • COOH 

7. Tyrosin, C 9 HnN0 3 , or /3-parahydroxyphenyl-a-aminopropionic 
acid. ' HO • C 6 H 4 • CH 2 • CH(NH 2 ) ■ COOH 

8. Serin, C3H7NO3, or /3-hydroxy-a:-aminopropionic acid. 

CH 2 (OH) • CH(NH 2 ) • COOH 

9. Cystin, C6Hi 2 N 2 4 S 2 , or dicysteine, or di- (/3-thio-a-aminopro- 
pionicacid) HOOC • CH(NH 2 ) • CH 2 • S — S • CH 2 • CH(NH 2 ) • COOH 

B. Monoaminodicarboxylic acids 

10. Aspartic acid, C 4 H 7 N0 4 , or a aminosuccinic acid. 

HOOC • CH 2 • CH(NH 2 ) • COOH 

11. Glutamic acid, C 5 H 9 NOi, or a-aminoglutaric acid. 

HOOC • CH 2 • CH 2 • CH(NH 2 ) • COOH 

1 The Chemical Constitution of the Proteins, Part I, 2d Ed., 1912. 



30 NUTRITION OF FARM ANIMALS 

C. Diaminomonocarboxylic acids 

12. Arginin, C 6 Hi 4 N40 2 , or «-amino-y-guanidin valerianic acid. 

HN = C/ NH2 

NH • CH 2 • CH 2 • CH 2 • CH(NH 2 ) • COOH 

13. Lysin, CoHi 4 N 2 2 or a, e-diaminocaproic acid. 

H 2 N • CH 2 • CH 2 • CH 2 • CH 2 • CH(NH 2 ) • COOH 

D. Heterocyclic compounds 

14. Histidin, C 6 H 9 N30 2 , or /3-imidazol-a-aminopropionic acid. 

CH 

^ \ 
N NH 

I I 

CH = C — CH 2 • CH(NH 2 ) • COOH. 

15. Prolin, C 5 H 9 N0 2 , or -pyrrolidin carboxylic acid 

CH 2 — CH 2 

I I 

CH 2 CH ■ COOH 

\ / 
NH 

16. Oxyprolin, or oxypyrrolidine carboxylic acid. 

QH 9 N0 3 

17. Tryptophan, CnHi 2 N 2 2 , or /3-indol-a-aminopropionic acid. 

C — CH 2 • CH(NH 2 ) • COOH 

/x 

C 6 H 4 CH 

\ / 
NH 

48. Synthesis of proteins. — Peptids. — Fischer and others 
have shown that the amino acids which result from the cleavage 
of the simple proteins may combine with each other, the NH 2 
of one uniting with the COOH group of the other with the 
elimination of one tnolecule of water. As many as 18 molecules 
of amino acids have been combined in this way, although the 
exact structure of the resulting compounds is still more or less 
uncertain. 

The compounds of the amino acids which have been prepared 
artificially have received the general name of peptids, the pre- 
fixes di-, tri-, etc., being used to indicate the number of amino 
acid molecules entering into the compound. The term poly- 



THE COMPONENTS OF PLANTS AND ANIMALS 31 

peptids is also commonly used as a general term for the more 
complex substances of this group. The latter show many of 
the reactions of the proteins or of their less modified deriva- 
tives. For example, many of them give the biuret reaction 
characteristic of the proteins, are precipitated by phospho- 
tungstic acid and undergo cleavage by appropriate proteolytic 
ferments. Moreover, some of the artificial polypeptids of known 
composition have also been isolated from the mixture of products 
resulting from the action of ferments upon the proteins. 

49. Conclusions. — Since, therefore, the same comparatively 
simple crystalline products are obtained as the final result of 
the complete hydrolysis of all the simple proteins, viz., the 
various amino acids enumerated in a previous paragraph (47), 
and since, on the other hand, these cleavage products may be 
synthesized to form substances closely resembling the proteins, 
it is believed that the protein molecule is built up of these 
amino acids, united in substantially the same way as in the 
artificially prepared polypeptids. In other words, it is be- 
lieved that the latter are the first steps toward the synthesis 
of proteins, or indeed that they may, from a systematic point 
of view, be regarded as the simplest of the proteins. 

It should be noted, however, that while the foregoing method of 
combination of the amino acids appears to be characteristic of the 
protein molecule, it is not the only form of combination in which 
nitrogen enters into it. For example, arginin, apparently a constit- 
uent of all proteins, contains an atom of imid nitrogen, HN. The 
proteins also contain amid nitrogen (i.e., NH 2 substituted for the OH 
of the carboxyl group) which yields ammonia on hydrolysis. Further- 
more, the proteins are capable of acting as polyacid bases and there- 
fore the molecule must contain numerous NH 2 end-groups such as 
that of the amids just mentioned or those of the diamino-acids like 
lysin and arginin. 

50. Proportions of cleavage products in different proteins. — 

While all the simple proteins yield, with a few exceptions, 
qualitatively the same cleavage products, the relative pro- 
portions of these " building stones " vary widely in proteins 
from different sources. This is strikingly illustrated by the 
following tabulation of the percentages of the various amino 
acids yielded by a number of proteins according to the researches 
of Osborne and his associates. 



32 



NUTRITION OF FARM ANIMALS 

Table 4. — Cleavage Products of Proteins 1 






1 < 


a 


3 
8 

H < 
D W 



S w 

N S 




O <! 

w w 


g 

p 

n 

< 



W 


i 
p 

« 
< 

b 

< 


« 
w S 

< O 


w 

P 

X 




eg 

K P 




% 


% 


% 


% 


% 


% 


% 


% 


% 


Glycin 


0.00 


O.89 


O.OO 


0.38 


0.0 


0.0 


0.00 


2.06 


0.68 


Alanin . . . 








2.00 


4-65 


13-39 


2.08 


2.22 


2.50 


1.50 


3-72 


2.28 


Valin . . ,. 








3-34 


0.24 


1.88 


— 


2.50 


0.90 


7.20 


0.81 


+ 


Leucin . . . 








6.62 


5-95 


19-55 


8.00 


10.71 


19.40 


9-35 


11.65 


II. 19 


Phenylalanin 








2-35 


1.97 


6-55 


3-75 


5-07 


2.40 


3.20 


3-i5 


3-53 


Tyrosin 








1.50 


4-25 


3-55 


i-55 


1.77 


2.20 


4-5o 


2.20 


2.16 


Serin . . . 








0.13 


0.74 


1.02 


o-53 


? 


? 


0.50 


? 


? 


Cystin . . 








o.45 


0.02 


? 


— 


? 


? 


? 


— 


— 


Prolin . . 








13.22 


4-23 


9.04 


3-22 


3-56 


4.00 


6.70 


5.82 


4-74 


Aspartic acid 








0.58 


0.91 


1.71 


5-30 


2.20 


1. 00 


i-39 


4-5i 


3.21 


Glutamic acic 


[ 






43.66 


23.42 


26.17 


I3.80 


9.10 


10.10 


15-55 


15-49 


16.48 


Tryptophan 








1. 00 


+ 


0.00 


+ 


+ 


+ 


1.50 


+ 


+ 


Arginin 








3.16 


4.72 


i-55 


IO.I2 


4.91 


3.01 


3-8i 


7-47 


6.50 


Lysin . . 








? 


1.92 


0.00 


4.98 


3-76 


8.10 


7.61 


7-59 


7.24 


Histidin . 








1.49 


1.76 


0.82 


2.42 


1. 71 


i-53 


2.50 


1.76 


2.47 


Ammonia . 








5.22 


4.01 


3-64 


1.99 


i-34 


1.32 


1.61 


1.07 


1.67 


Total . . 


84.72 


59-68 


88.87 


58.12 


48.85 


56.46 


66.92 


67.29 


62.15 



The results shown in the foregoing table are typical. In a 
few proteins, certain amino acids have not been found at all. 
For example, no glycin has been found among the products of 
the hydrolysis of gliadin, zein, albumin or casein and no lysin 
among those of gliadin or zein. Furthermore, the proportion of 
the various cleavage products is quite variable in the different 
proteins, one of the most striking instances being that of glu- 
tamic acid which ranges from nearly 44 per cent in the gliadin 
of wheat to a little over 9 per cent in egg albumin, and is no- 
tably more abundant in vegetable than in animal proteins. 

51. Classification. — For the present purpose, it seems super- 
fluous to enter into a full description of the various simple pro- 

1 The sign + signifies that the substance was present but was not quantitatively 
determined. A blank simply indicates that the ingredient in question was not 
determined but does not show that it was not present. 



THE COMPONENTS OF PLANTS AND ANIMALS 33 

teins. The principal groups into which they are subdivided are 
designated as follows: — * 

a. Albumins. — These are simple proteins soluble in pure 
water and coagulable by heat. Besides the familiar egg al- 
bumin, they include the albumins of blood serum and of milk 
serum. Albumins have also been found in small amounts in 
a great variety of seeds, including those of wheat, rye, barley, 
pea, vetch, soybean and cowpea. 

b. Globulins. — The globulins are simple proteins insoluble 
in pure water but soluble in neutral solutions of salts of strong 
bases with strong acids. Globulins are found in the lymph 
and the blood serum and in the muscles and other organs, but 
they appear to be especially characteristic of the vegetable 
kingdom, occurring in considerable amounts in a large number 
of seeds. Osborne 1 gives a list of 15 globulins occurring in 24 
different species of seeds and enumerates 12 additional species 
which contain globulins to which no distinctive names have 
yet been given. 

c. Glutelins. — These are defined as simple proteins insoluble 
in all neutral solvents but readily soluble in very dilute acids 
and alkalies. The only well-defined members of this group at 
present known are the glutenin of wheat and the oryzenin of 
rice, although there seems reason to believe that similar pro- 
teins exist in the seeds of other cereals. 

d. Prolamins, or alcohol-soluble proteins. — The typical mem- 
ber of this group is the gliadin of wheat and the name has 
been applied by some authors to the entire group, but the 
term prolamins, proposed by Osborne, seems preferable. The 
prolamins are soluble in relatively strong alcohol (70-80 percent) 
but insoluble in water, absolute alcohol and other neutral sol- 
vents. They are characteristic of the seeds of the cereals, the 
principal prolamins being the gliadin of wheat and rye, the 
hordein of barley, the zein of maize and the bynin of malt. 

e. Albuminoids. — This name, formerly used to a consider- 
able extent as practically synonymous with proteins, is now 
applied to two groups of nitrogenous substances which have 
been otherwise designated as the collagens, or gelatinoids, and 
the keratins. Albuminoids are defined as simple proteins which 
possess essentially the same chemical structure as the other 

1 The Vegetable Proteins, p. 78. 
D 



34 NUTRITION OF FARM ANIMALS 

proteins but are characterized by great insolubility in all 
neutral solvents. They form the principal organic constituents 
of the skeletal structures of animals and of their external cover- 
ing and its appendages and hence have also been called sclero- 
proteins. This definition does not provide for gelatin, which 
is, however, an artificial derivative of collagen. Besides gela- 
tin the more important members of this group are chondrin, 
or collagen, which constitutes the organic basis of cartilage and 
bone; elastin, the characteristic component of the ligaments; 
and the keratins of the epidermal tissues such as hair, wool, 
feathers, horns, hoofs, etc. 

The conjugated proteins 

52. Nucleoproteins. — In the scheme of classification here 
followed (41), the nucleoproteins are defined as follows : " These 
proteins are especially characteristic of the nucleus of the 
vegetable and animal cell (74). They consist of protein mole- 
cules united with one or more of the compounds known as 
nucleic acids. These are complex organic compounds contain- 
ing a phosphoric acid radicle and also a xanthin group." 

The simple proteins of the nucleoproteins apparently may be 
of quite diverse nature and belong to various groups of the 
simple proteins. The special interest of the nucleoproteins 
attaches to the nucleic acids entering into their composition. 

53. Nucleic acids. — These compounds contain in addition 
to carbon, hydrogen, nitrogen and oxygen the element phos- 
phorus. Their constitution has not yet been fully worked out, 
but their cleavage yields four classes of products, viz., 

i. Xanthin, or purin, bases 

2. Pyrimidin bases 

3. A pentose carbohydrate 

4. Phosphoric acid 

According to the recent investigations of Levene and others, 
the nucleic acid molecule may be regarded as built up from 
nucleosids, or glucosid-like combinations of a pentose carbohy- 
drate with a purin or pyrimidin base. By the union of such a 
nucleosid with phosphoric acid there is formed a nucleotid. 
Finally, the most common nucleic acids are tetranucleotids. 



THE COMPONENTS OF PLANTS AND ANIMALS 35 

which seem always to contain both purin and pyrimidin nucleo- 
sids. 

54. Glycoproteins. — The glycoproteins are defined as " Com- 
pounds of the protein molecule with a substance or substances 
containing a carbohydrate group other than a nucleic acid. 
The principal compounds of this group are the mucins and the 
mucoids." 

55. Phosphoproteins. — These are defined as compounds of 
the protein molecule with some, as yet undefined, phosphorus- 
containing substance other than a nucleic acid or lecithin. 
The casein, or rather caseinogen, of milk is one of the most 
familiar and important of this group. 

56. Haemoglobins. — The haemoglobins are compounds of 
the protein molecule with haematin or some similar substance, 
and constitute the red coloring matter of the blood. 

57. Lecithoproteins. — Compounds of the protein molecule 
with lecithins. 

The derived proteins 

58. Primary protein derivatives. — Derivatives of protein ap- 
parently formed through hydrolytic changes which involve only slight 
alterations of the molecule. 

Proteans. — Insoluble products which apparently result from the 
incipient action of water, very dilute acids or enzyms. 

Metaproteins. — Products of the further action of acids and alkalies 
whereby the molecule is so far altered as to form products soluble in 
very weak acids and alkalies but insoluble in neutral fluids. This 
group will thus include the familiar "acid proteins" and "alkali pro- 
teins," not the salts of proteins with acids. 

Coagulated proteins. — Insoluble products which result from (1) the 
action of heat on their solutions, or (2) the action of alcohols on the 
protein. 

59. Secondary protein derivatives. — Products of the further 
hydrolytic cleavage of the protein molecule. 

Proteoses. — Soluble in water, uncoagulated by heat, and pre- 
cipitated by saturating their solutions with ammonium or zinc 
sulphate. 

Peptones. — Soluble in water, uncoagulated by heat but not pre- 
cipitated by saturating their solutions with ammonium sulphate. 

Peptids. — Definitely characterized combinations of two or more 
amino acids, the carboxyl group of one being united with the amino 
group of the other with the elimination of a molecule of water (48) . 



36 NUTRITION OF FARM ANIMALS 

§ 5. The Non-proteins 

60. Occurrence. — In addition to the proteins, both plants 
and animals contain a great variety and sometimes relatively 
considerable amounts of nitrogenous compounds of the most 
diverse nature. While the occurrence of such compounds, es- 
pecially in feeding stuffs, was known from an early day, it was 
long assumed that the amounts present were relatively insignifi- 
cant and that no material error was involved in regarding all 
the nitrogen of a feeding stuff as existing in the form of protein. 
Accordingly, the total nitrogen multiplied by the conventional 
factor 6.25 and designated as " crude protein " was taken as 
representing the true protein content of the material. The 
researches of Scheibler, E. Schulze and Kellner in the seventies, 
however, showed that this was far from being the case. It 
was found that nitrogenous substances other than protein 
were very widely distributed and that sometimes as much as 
one-third or even one-half of the total nitrogen of feeding 
stuffs existed in these non-protein compounds. These results 
have been fully confirmed by subsequent investigations and it 
has therefore become necessary to distinguish between these 
substances and the true proteins. 

61. Definition. General properties. — While these nitrog- 
enous compounds other than protein are of the most varied 
nature, they all differ from the proteins in having a much less 
Complex molecular structure. Many are comparatively simple, 
crystalline substances, most of them readily soluble in water 
and diffusible, and they appear distinctly inferior in nutritive 
value to the proteins. It is a matter of practical convenience, 
therefore, to have a group name by which to distinguish them 
and for this purpose the term non-proteins has been proposed. 
It is, of course, a contraction for non-protein nitrogenous sub- 
stances and means simply substances which contain nitrogen 
but are not proteins. It therefore includes a great variety of 
compounds and may be considered as in a sense a cover for 
our ignorance of their exact nature. The more important 
groups of non-proteins are: — 

The nitrogenous muscle extractives 
The nitrogenous lipoids 



THE COMPONENTS OF PLANTS AND ANIMALS 37 

The nitrogenous glucosids 
Alkaloids and organic bases 
Amino acids and amids 
Nitrates and ammonium salts 

62. The muscle extractives. — The more important nitrog- 
enous muscle extractives are creatin, creatinin and the purin 
bases xanthinand hypoxanthin. 

63. Nitrogenous lipoids. — As noted (37-39), the lipoid 
group includes a number of compounds, classed as phosphatids 
and cerebrosids, which contain a nitrogenous group in combi- 
nation with fatty acid radicles. The most familiar members of 
this group are the lecithins. The actual amounts of these sub- 
stances contained either in the animal or plant are small and 
their nitrogen does not constitute any important fraction of 
the total nitrogen of the body or of the feed. 

64. Alkaloids and organic bases. — Alkaloids are compara- 
tively rare in agricultural plants, the seeds of the lupine forming 
the principal exception. The organic bases, on the other 
hand, appear to be somewhat widely distributed. In addition 
to the so-called " hexon bases " arginin, lysin and histidin, de- 
rived from the proteins and nucleo-proteins, the bases cholin, 
betain, trigonellin and stachydrin have been found in a variety 
of plants. 

65. Nitrogenous glucosids. — The substances of this group 
are characteristic of the vegetable kingdom. They contain 
a variety of nitrogenous compounds coupled with simple sugars. 
The nitrogenous glucosids do not appear to be especially abun- 
dant in the ordinary feeding stuffs of domestic animals and 
where they do occur are distinguished rather by their specific 
physiological effects than by their nutritive value in the or- 
dinary sense. E. Schulze 1 mentions seven bodies of this class 
which have been found in various plants. 

66. Amino acids and amids. — These substances are by far 
the most abundant forms of non-protein in vegetable materials. 
The first one to be discovered was asparagin, in 1805, in aspar- 
agus shoots, and this substance has since been found in a large 
number of plants or parts of plants. Glutamin, a second 
amid, is also of frequent occurrence in plants. 

1 Jour. Landw., 52 (1904), 305. 



38 



NUTRITION OF FARM ANIMALS 



Asparagin and glutamin are respectively the amids of aspartic and 
glutamic acids, both of which are constituents of the protein molecule. 



COOH 



COOH 



COOH 



COOH 



CH 2 



CH 2 



CH 2 



CH 2 



CH • NH 2 
COOH 

Aspartic acid 



CH • NH 2 



CH 2 



CO • NH 2 CH • NH 2 

Asparagin 

COOH 

Glutamic acid 



CH 2 

I 

CH • NH 2 



CO • NH 2 

Glutamin 



It has thus come about that the term amids has been more 
or less commonly used as a general designation for the non-pro- 
tein nitrogenous substances found in feeding stuffs. The usage, 
however, is unfortunate. The word amid denotes a distinct 
class of chemical substances of which only asparagin and glu- 
tamin appear to be especially common in plants, while the 
latter contain a variety of nitrogenous substances which are 
not amids at all. The general term non-protein proposed above, 
therefore, seems preferable. 

In addition to asparagin and glutamin there have been found 
in feeding stuffs a large number of the cleavage products of the 
proteins. E. Schulze **■ enumerates ten amino acids, viz., valin, 
leucin, isoleucin, phenylalanin, tyrosin, prolin, tryptophan, 
arginin, lysin and histidin, besides the purin bases xanthin, hy- 
poxanthin, adenin and guanin, as well as guanidin, allantoin 
and carnin, as having been isolated from various vegetable ma- 
terials. Hart and Bentley 4 found that from 50 to 70 per cent 
of the water-soluble nitrogen of a variety of feeding stuffs ex- 
isted as amino acids or peptids, while the amid nitrogen proper 
amounted to only 10 to 20 per cent. 

Occurrence. — These substances evidently stand in a close 
relation to the protein metabolism of the plant. They appear 
to be in part intermediate products in the synthesis of protein 
from nitrates and ammonium salts and in part to be formed in 
the cleavage of proteins necessary for their translocation and 
resynthesis during the processes of growth. They are especially 



1 Jour. f. Landw., 52 (1904), 305. 2 Ztschr. Physiol. Chem., 45 (1905), 38. 

3 Ztschr. Physiol. Chem., 47 (1906), 507. 4 Jour. Biol. Chem., 22 (1915), 477- 



THE COMPONENTS OF PLANTS AND ANIMALS 39 

abundant, therefore, where growth is going on most rapidly. 
Young and succulent feeding stuffs, such as pasture grass, green 
soiling crops and the like, accordingly contain a considerable 
proportion of their nitrogen in the non-protein form. As plants 
approach ripeness, the proportion of non-protein to protein 
nitrogen becomes less, so that mature hay, straw and the like 
are relatively poor in non-proteins. This is especially true of 
seeds, whose nitrogen is contained chiefly in the reserve pro- 
teins, although small amounts of various non-proteins are also 
found. One class of feeding stuffs relatively rich in non-protein 
is the roots and tubers, in which the conversion of inorganic 
nitrogen into protein seems to be incomplete and in which the 
non-protein serves as a nitrogenous reserve for the growth of 
the succeeding year. Finally, feeding stuffs which have under- 
gone fermentation, such as silage, show a relative increase of the 
non-protein nitrogen over that of the original material. 

67. Nitrates and ammonium salts. — Occasionally somewhat 
considerable amounts of nitrates or of ammonium compounds 
are found in vegetable material, especially when the supply of 
soluble nitrogen compounds in the soil is abundant. In such 
cases they are to be regarded as materials taken up in excess 
of the immediate needs of the plant. 

§ 6. Sundry Ingredients 

68. Number and significance. — In the foregoing sections 
the groups of substances which constitute the animal body or, 
in the form of feed, supply the matter and energy for its growth 
and maintenance have been considered. It is hardly necessary 
to say, however, that these four groups, the carbohydrates, 
fats, proteins and non-proteins, are very far from comprising all 
the constituents of animals or plants. 

In the animal body the physiological chemist has recognized 
relatively small amounts of a vast number of substances of 
the most varied nature. Some of these are derived quite di- 
rectly from the proteins, fats or carbohydrates and these will be 
considered to a greater or less extent in studying the changes 
which these substances undergo in the body. Others, while of 
great physiological importance, have little direct relation to the 
processes of nutrition. 



40 NUTRITION OF FARM ANIMALS 

Similarly, plants contain a great variety of ingredients not 
strictly belonging to any of the four main groups. In the 
aggregate, these substances do not often add greatly to the po- 
tential food value of feeding stuffs, but, on the other hand, 
they may in some cases considerably modify their palatability 
or the activity of the various processes of nutrition and so affect 
the actual results of feeding. Until recently these secondary in- 
gredients of feeding stuffs have received comparatively little 
attention. 

69. Organic acids. — Aside from the small amounts of free 
fatty acids occurring in most native fats, both animal and vege- 
table (29, 33), the acids of this series are seldom or never found 
in native feeding stuffs. In those feeding stuffs which have 
undergone bacterial fermentation, however, notably in the case 
of silage, more or less acetic and butyric acids occur, but the 
principal acid product of such fermentations is lactic acid, 
C 3 H 6 03. The same acids, along with formic and propionic 
acids and minute amounts of ethyl aldehyde, likewise result 
from the bacterial fermentation of the carbohydrates of the 
feed in the paunch of ruminants and thus constitute a not un- 
important portion of the non-nitrogenous material resorbed 
from the feed (128-132). The principal organic acids found 
in native feeding stuffs are malic, tartaric, citric and oxalic, 
usually as the potassium, sodium or calcium salts. 

70. Ethereal oils. — The so-called ethereal oils are substances 
of complex molecular nature, somewhat resembling the true 
oils in their physical properties but which can readily be dis- 
tilled in a current of steam. Familiar examples are the so-called 
oils of peppermint, lemon, anise, and the like. It is not known 
that they have any direct nutritive value themselves but they 
add to the flavor and aroma of feeds and in some cases are be- 
lieved to stimulate the digestive processes. The agreeable 
odor of good hay, for example, and doubtless in part its fa- 
vorable dietetic effect, is due to substances resembling in prop- 
erties the ethereal oils. To the same class of ethereal oils 
belong the oils of mustard, onion and garlic, whose deleterious 
effect upon the flavor of dairy products is so well known. 

71. Flavoring substances in general. — What is called the 
flavor of a food or feeding stuff depends largely upon the action 
on the sense of smell of a great variety of substances either con- 



THE COMPONENTS OF PLANTS AND ANIMALS 41 

tained in the material originally or, especially in the case of 
human foods, artificially added or developed during cooking. 
Besides ethereal oils, stock feeds contain a great variety of 
bitter or astringent substances, gums, waxes, resins, etc., etc., 
of whose properties and physiological effects little or nothing is 
known. The flavor and palatability of feed, as already indi- 
cated, are usually dependent upon these accessory ingredients, 
while the fact that palatability is an important factor in nu- 
trition aside from any direct nutritive effect will appear in later 
discussions. 

72. Vitamins : Growth substances. — Much attention has 
been devoted during the past few years to an important but as 
yet rather ill-defined group of food constituents called by some 
investigators vitamins and by others growth substances. These 
substances, however, are known by their effects rather than by 
their chemical properties and may therefore be more appropri- 
ately considered in their relations to the requirements for 
maintenance and growth (438, 498, 738). 



CHAPTER II 
THE COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 

§ i. The Cell 

73. Definition. — The cell may be defined as the biological 
unit of all life. It is the simplest form in which living matter 
can exist. It might be regarded as bearing somewhat the same 
relation to the animal or plant that the atom does to a complex 
organic molecule such as that of one of the proteins for example. 
It is seen in its simplest form in unicellular organisms (protozoa) 
in which all the functions of life are performed by a single cell. 
As we ascend in the scale of organization a number of cells are 
united to form one individual, the various vital functions being 
to a greater or less extent distributed among different cells or 
cell groups. In the higher organisms the cells are numbered 
by myriads, while the physiological division of labor and the 
corresponding differentiation of form reach an extreme. The 
organization of such an individual has been likened to that of 
a state or nation, in which the functions of the single citizen 
are highly specialized. A few of the diverse forms of animal 
cells are represented in Fig. i. 

74. Structure of cells. — The typical cell consists of the 
cell body, or cytoplasm, within which is the nucleus. The 
peripheral portion of the cytoplasm is often somewhat more 
compact than the remainder and serves to separate the cell 
from its surroundings. Sometimes a distinct membrane, or 
cell wall, is developed, especially in plants, although this is not 
a necessary part of the cell. The name protoplasm is often 
applied to the entire active part of the cell, i.e., to cytoplasm plus 
nucleus. All forms of life, vegetable as well as animal, are in- 
dissolubly associated with and manifested through the activities 
of protoplasm, which was called by Huxley the physical basis 
of life. It should be understood, however, that the word pro- 
toplasm is not a chemical but a biological term. It is a struc- 

42 

y 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 43 

ture rather than a substance. Moreover, there is not one pro- 
toplasm, common to all cells, but as many protoplasms as there 
are kinds of cells. 

There is a more or less sharp differentiation between the 
functions of the nucleus and those of the cytoplasm. The 
nucleus appears to be especially concerned in cell reproduction, 




Fig. 1. — Different types of cell composing the body. (Hadley, The Horse 
in Health and Disease.) 

the formation of a new cell beginning with a division of the 
nucleus of an existing c«U and being followed by a division 
of its cytoplasm. The main function of the cytoplasm, on 
the other hand, seems to be the nutrition of the cell, and the 
presence of at least a minimum amount of it is essential to the 
continued existence of the nucleus. For the present purpose, 
it is unnecessary to attempt a further discussion of those finer 
details of the structure of the cell which have been worked out 
by the labors of the histologist and physiologist. 



44 NUTRITION OF FARM ANIMALS 

75. Composition of protoplasm. — The chemical constitution 
of living protoplasm is unknown, partly because it is undoubtedly 
very complex but chiefly because of its instability and the im- 
possibility of isolating it without at the same time destroying 
its life. Moreover, it doubtless varies materially in cells of 
different types. The proteins, perhaps combined with each 
other into " giant molecules," undoubtedly constitute the 
basis and predominating ingredient of protoplasm, but certain 
lipoids (lecithins and cholesterins), ash ingredients (electrolytes), 
and perhaps glycogen and other carbohydrates, in addition, 
of course, to water, appear to be also essential constituents. In 
the cytoplasm, the simple proteins (41) seem to predominate, 
while the nucleus is especially characterized by the presence of 
the nucleoproteins (52). 

76. The cell wall. — As already indicated, the protoplasm 
often develops a cell wall. So far as concerns the species of 
plants which serve as feed for farm animals, it may be said 
that a vegetable cell is always surrounded by a cell wall the 
basic ingredient of which is the carbohydrate cellulose, a sub- 
stance not found in the bodies of the higher animals. 

In the young and growing parts of plants, the cell wall is thin 
and consists substantially of cellulose only. In certain parts 
of plants, such as the cotyledons and endosperms of seeds or 
the tissues of succulent roots and tubers, the cell wall remains 
comparatively thin even in mature tissue. In other parts of 
the plant, on the contrary, it becomes very much thickened by 
the deposition of additional cellulose and especially of substances 
other than cellulose. These other substances, which appear 
to be essentially carbohydrates or their derivatives, are of two 
general kinds. The first of these is the hemicelluloses (18), 
which are more readily attacked by hydrolyzing agents than 
pure cellulose and which constitute to a large extent a deposit 
of reserve material and include both hexosans and pentosans. 
The second consists of substances belonging to the lignin and 
cutin groups (19, 20), which serve to impart strength and rigidity 
along with more or less impermeability to the cell wall. They 
are, therefore, particularly abundant in older plants as com- 
pared with younger ones and in those organs which serve to 
support the plant, such as the stem. The extreme form of the 
thickened cell wall is seen in wood. A few of the numerous 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 45 

forms of vegetable cells are illustrated in Figs. 43-45 of 
Chapter XV. 

77. Cell enclosures. — In addition to the essential constitu- 
ents of the cytoplasm and nucleus there are observed in cells 
a variety of other substances designated as subsidiary ingredi- 
ents or cell enclosures. These may consist of food material 
which has entered the cell and is on its way to being incor- 
porated into the molecules of protoplasm, or, on the other hand, 
of waste products of cell activity on their way to being ex- 
creted from the cell into the surrounding medium. Moreover, 
many cells have the power of storing up surplus food, especially 
non-nitrogenous substances, as reserve material. Such material 
is not usually regarded as constituting a part of the protoplasm 
but as being simply included in it mechanically. 

The most common cell enclosure in the animal is fat, which 
is contained in large quantity in certain connective tissue cells 
and constitutes the reserve fuel material of the animal body, 
the storage of carbohydrates (glycogen) being much more 
limited in amount. While some important groups of plants 
also store up large amounts of fat in their seeds, nevertheless 
the predominating reserve materials in the vegetable kingdom 
are carbohydrates, including the reserve carbohydrates of the 
cell wall and, as a cell enclosure, starch. Starch is found in 
all parts of plants, but is especially abundant in seeds and in 
the starchy roots and tubers, where large amounts of this sub- 
stance are stored up. Illustrations of plant cells containing 
starch are afforded by Figs. 43-45 of Chapter XV. 

Both because of the chemical composition of the cell wall 
and the nature of the cell enclosures, carbohydrates are quan- 
titatively the predominating ingredients of most plants, while 
animal cells and tissues are chiefly proteid or fatty in character. 

§ 2. Animal Tissues and Organs 

78. Classification. — Not only do the cells of higher animals 
show extreme differentiation of form and function, but cells 
having the same general nature and office are associated together 
to form what are called tissues, such as nerve tissue, muscular 
tissue, connective tissue and the like, each serving its own 
specific purpose. These tissues, again, are grouped together 



46 NUTRITION OF FARM AMIMALS 

to form organs, such as the muscles, heart, lungs, stomach, 
liver and the like, each performing its special part in the com- 
plex interplay of activities necessary for the life of the organism 
as a whole. 

Since this is not a treatise on anatomy, it is unnecessary to 
consider in detail all the diverse types of tissue or all the various 
organs making up the body. It is desirable, however, that the 
student of nutrition should acquire some notion of the chemical 
make-up of the various parts of the body. For this purpose it 
will be convenient to use the following scheme, based chiefly 
on the functions performed by the different groups of tissues, 
which ignores to some extent the distinction between tissues 
and organs and which does not pretend to be an exact or ex- 
haustive classification. 

First : The supporting tissues, including bone, tendon, carti- 
lage, ligament, elastic tissue, etc. 

Second : The tissues of motion, including the muscular 
tissues and the nerve tissues or the nervous system. 

Third : The tissues of alimentation, including the tissues 
and organs concerned in digestion, resorption, circulation, 
respiration and excretion. 

Fourth : The epidermal tissues. 

Fifth : The reserve tissues, including, besides adipose 
tissue, those tissues in which glycogen is more or less abun- 
dantly stored. 

The supporting tissues 

79. Intercellular substance. — In the bodies of the higher 
animals certain tissues show an enormous development of the 
so-called intercellular substance, so that the cells, instead of 
closely adjoining each other, are imbedded in a mass of non- 
cellular material which may vary greatly in consistency. Some- 
times this intercellular substance is entirely homogeneous but 
it usually contains a greater or less number of fibers imbedded in 
a homogeneous basis. By virtue of the special properties of 
the intercellular substance, tissues of this sort perform pri- 
marily mechanical functions, maintaining the form of the body 
or serving to connect and support other tissues, while the cells 
themselves serve principally to produce and maintain the inter- 
cellular substance. The organic basis of the latter is the group 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 47 

of proteins called in Chapter I the albuminoids or the seleno- 
proteins (51 e) accompanied by varying amounts of mineral 
matter, and, of course, a considerable proportion of water. 

80. Bone. — Bone is the most familiar example of the sup- 
porting tissues of the animal body. In the young embryo the 
bones first appear as cartilaginous structures consisting of 
rounded cells imbedded in a homogeneous intercellular substance 
containing also fibers and consisting mainly of collagen (51 e). 
As development advances, the process of ossification begins, the 
homogeneous substance of the cartilage taking up inorganic salts, 
chiefly calcium phosphate, while the fibers of the cartilage are 
stated not to take part in this process. In addition to mineral 
matter, the bones store up also a variable amount of fat. Ma- 
ture bone, therefore, aside from its fat, consists of a basis of 
organic matter largely impregnated with mineral matter. The 
presence of these two classes of constituents is readily demon- 
strated by the familiar experiments in which, on the one hand, 
the mineral matter is removed by immersion in dilute acid 
leaving behind the flexible cartilage, or, on the other hand, 
the organic basis of the bone is destroyed by heating, leaving 
the so-called bone ash. 

Ossification has not been completed at birth but continues to a 
greater or less extent up to full maturity Moreover, it is not carried 
to the same extent in all bones nor in different parts of the same bone. 
Consequently, both the percentages of ash and of fat and the propor- 
tion of water to dry matter in bones may vary within wide limits, so 
that it is impossible to state an average composition. The extremes 
of 1 5 per cent and 44 per cent have been found for the average water 
content of the entire skeleton of the dog and even wider variations 
have been reported in the case of man. Compact bones contain less 
water than more spongy ones. 

In general it may be said that from one-half to two-thirds of 
the dry, fat-free bone consists of ash. About three-fourths of 
the remainder is stated to consist essentially of albuminoids, or 
collagens, yielding gelatin when treated with hot water, es- 
pecially under pressure. It is evident, therefore, that the 
skeleton of an animal contains not only a large share of the 
total ash of the body but a not inconsiderable portion of its 
nitrogenous constituents as well. On the average of the ten 
animals analyzed by Lawes and Gilbert (97), 77.78 per cent of 



4 8 



NUTRITION OF FARM ANIMALS 



the total ash of the entire animal and 83.01 per cent of the ash 
of the carcass was contained in the bones. Of the total nitro- 
gen of the carcasses of eight of these animals 18.04 P er cen t 
was contained in the bones. Corresponding data for the entire 
animal are not recorded. 

81. Bone ash. — But while the composition of bone itself 
is quite variable, that of the bone ash is notably constant even in 
different species. The predominant ingredient is tri-calcic 
phosphate but it contains, also, calcium carbonate as well as 
phosphates and carbonates of magnesium and other bases. 
The average composition given by Zalesky ' is as follows : — 

Table 5. — Composition of Bone Ash of Different Species 



Calcium phosphate . . 
Magnesium phosphate 
Calcium combined with 
CI, Fl . \ . . . . 
Carbon dioxid .... 



C0 2 



Man 


Cattle 


Guinea Pig 


% 


% 


% 


83.89 


86.09 


87.32 


1.04 


1.02 


1 -05 


7-65 


7-30 


7-03 


5-73 


6.20 





Turtle 

% 

85.98 
1.36 

6.32 
5-27 



More detailed analyses by Gabriel 2 yielded the following 
results : — 

Table 6. — Composition of Bone Ash 





Teeth of 


Bones of 


Bones of 


Bones of 




Cattle 


Man 


Cattle 


Geese 




% 


% 


% 


% 


CaO . . . . . 


50.76 


5I-3 1 


51.28 


51.01 


MgO 


1.52 


0.77 


1.05 


1.27 


K 2 


0.20 


0.32 


0.18 


0.19 


Na 2 


1. 16 


1.04 


1.09 


1. 11 


HoO 


2.21 


2.46 


2-33 


3-OS 


P2O5 


38.88 


36.65 


37.46 


38.19 


C0 2 


4.09 


5-86 


5.06 


4.11 


CI 


0.05 


0.01 


0.04 


0.06 




98.87 


98.43 


98.49 


98.99 



1 Neumeister ; Lehrbuch der Physiologischen Chemie, 1897, p. 456. 
2 Ztschr. Physiol. Chem., 18 (1894), 257. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 49 

The small amounts of magnesium, sodium, potassium, carbon 
dioxid and chlorin appear to be as essential ingredients of bone 
ash as its calcium or phosphorus. 

82. Cartilage, ligament, tendon, elastic tissue. — Not all 
of the cartilaginous ground work of the skeleton as laid 
down in the embryo is converted into bone. In particular, the 
end surfaces of bones at a joint consist of cartilage, which in 
other cases forms a connecting link between adjoining bones, 
as, for example, the cartilage connecting the ribs with the 
breast bone, thus allowing a limited degree of motion. At the 
joints proper, the bones are held in place, and the direction and 
extent of their motions limited, by the ligaments, while the 
muscles which serve to impart motion to the various parts of 
the body are attached to the bones by means of tendons. In 
many cases the intercellular substance of the supporting tissue 
contains fibers of elastin. When these fibers are abundant the 
tissue is elastic in contrast to the ligaments and tendons of the 
joints, which are almost inextensible. A striking instance is 
afforded by the elastic band (Ligamentum nucha) which runs 
along the back of the neck of quadrupeds and supports the 
weight of the head. Another example is furnished by the layer 
of elastic tissue contained in the walls of the arteries which 
gives them a certain degree of resilience to the pressure of the 
blood pumped by the heart. 

The " organic " portion of all these forms of supporting tis- 
sue, like the organic portion of the bones, consists essentially of 
different proteins belonging to the group of albuminoids. 

83. Connective tissue. — This name is sometimes applied 
to all the various forms of supporting tissue, since they also 
serve to connect the various organs of the body. In a more 
ordinary and limited sense, however, it is used to designate a 
form of supporting tissue of which the most familiar example 
is the tissue lying between the skin and the underlying muscles, 
or lean meat, and serving to connect them together. A more 
careful examination shows that this subcutaneous connective 
tissue is continuous with other similar tissue which extends 
between the single muscles and serves at the same time to de- 
limit them and connect them. Not only so, but this sheath 
of connective tissue extends into the muscle itself, dividing it 
into muscular bundles or fasciculi and these again into secondary 



5° 



NUTRITION OF FARM ANIMALS 




If 

Fig. 2. - 
One end of a 
muscle fiber. 
(Hough and 
Sedgwick, 
The Human 
Mechanism.) 



fasciculi. The connective tissue of the interior of the muscle 
unites at the ends and is continuous with a form of connective 
tissue already mentioned, viz., the tendons, by 
means of which the muscles are attached to the 
bones (Fig. 2). 

A similar sheath of connective tissue surrounds 
the internal organs of* the body and extends into 
them, forming a framework which supports the 
active tissues of these organs as well as the blood 
vessels, nerves, lymphatics, etc., so that it may be 
said in a broad general way that the body of a 
higher animal consists of a variety of active tissues 
and organs contained in and supported by connec- 
tive tissue and the other forms of supporting tissue 
already described. 

Like other forms of supporting tissue, the connec- 
tive tissue consists of cells which have produced a 
relatively large amount of intercellular substance, 
which in connective tissue consists chiefly of fibers. Chem- 
ically, it is composed of collagen. Cells of connective tissue, 
however, may also store up within themselves large amounts 
of fat (94). 

Tissues of motion 

84. The muscles. — Both the external movements of an 
animal and those of the internal organs are effected by means 
of the muscles, and the muscular tissue is preeminently the 
tissue of motion. Moreover, the muscles make up a large part 
of the entire mass of the body of a lean animal and furnish 
nearly all the protein contained in the edible portion of the 
carcass. The composition of muscle and muscular tissue, there- 
fore, is of special interest. 

85. Structure of muscles. — The smallest anatomical element of 
muscular tissue is the single muscle fiber. This is a highly specialized 
and greatly elongated, thread-like cell one to one and a half inches 
long and having a diameter of from .0004 to .004 inch. It is en- 
closed in a very thin transparent membrane and contains many 
nuclei. A large number of these fibers — hundreds or even thousands 
— are bound together to form a fasciculus, the fibers running length- 
wise and overlapping each other, being generally shorter than the 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 51 



fasciculus. These fasciculi, as stated in a previous paragraph (83), 
are surrounded by connective tissue and united into larger fasciculi, 
or bundles, each with its envelope of connective tissue, these bundles 
again being united to form the individual muscles. The connective 
tissue serves also to carry the blood vessels, nerves and lymphatics 
with which the muscle is abundantly supplied, and, moreover, may 
contain larger or smaller accumulations of fat. 
Evidently, then, the muscle as a whole, and 
even more the collective muscles making up 
the lean meat of an animal, are far from consti- 
tuting a homogeneous material. 



86. Composition of muscles. — If the 
term muscular tissue be limited to the 
ultimate muscular fibers which are the ac- 
tive agents in producing motion, consider- 
ing the other structural elements of the 
muscle as accessory, it may probably be 
said in a general w r ay that it consists essen- 
tially of water, protein, meat extractives 
and the various lipoids and electrolytes 
found in greater or less amounts in all 
protoplasm. But such a limitation of the 
term muscular tissue, however rational from 
an anatomical standpoint, is little suited 
to the present purpose. In the nutrition muscle fiber. (Hough 
of the animal, material is required to build Human'MechanismO ^ 
up the entire muscular system, with all 
its accessory structures, and not merely for the production of 
the muscle fibers, and we are concerned, therefore, with the 
composition of the muscles as a whole — i.e., of the lean meat — 
rather than with that of the ultimate muscle-fibers. 

Since, however, the lean meat contains a variety of tissues 
aside from muscular tissue in the narrower sense — connective 
tissue, nerves, blood and lymph vessels, etc. (85) , with more or 
less of the fluid contents of the latter — it is evident that its 
composition is likely to be variable. Moreover, the lean meat, 
especially of fat animals, contains a considerable and variable 
amount of fat even after all the fat tissue which it is practicable 
to separate mechanically has been removed. This fat, how- 
ever, forms no part of the muscle proper but is simply a deposit 




Fig. 3. — Part of a 



52 



NUTRITION OF FARM ANIMALS 



of reserve material. It is contained in minute masses of adipose 
tissue (94) developed between the muscle bundles or even 
between the individual muscular fibers and differing only in 
size from the larger masses which may be trimmed off or re- 
moved with the scalpel. It is necessary to distinguish, there- 
fore, between lean meat in the commercial sense, with its vary- 
ing content of fat, and lean meat in the stricter scientific sense, 

i.e., the fat-free muscle. The com- 
position of the latter may be ascer- 
tained either by actually removing 
the fat from the ordinary trimmed 
meat by means of a • solvent and 
analyzing the residue or, more con- 
veniently, by analyzing the fresh 
meat and removing the fat arithmet- 
ically, i.e., by calculating the com- 
position of the fat-free muscle. 

87. Composition of fat-free muscle. 
— The composition of the fat-free 
lean meat of butchers' cuts has been 
determined by Henneberg, Kern and 
Wattenberg 1 for two old sheep and 
six younger ones ranging from 6J to 
28 months old, and Jordan 2 has de- 
termined the composition of the lean 
meat of the entire carcasses of four steers. 




Fig. 4. — Fat cells in muscle. 
(Bailey's Cyclopedia of Ameri- 
can Agriculture.) 



Table 7. — Average Composition of Fat-free Lean Meat of Sheep 





Old Sheep 


Lambs 






No. 8 
Lean 


No. 8 

Very 

fat 


6J 

mos. 

old 


13 
mos. 
old 


22 
mos. 
old 


28 
mos. 
old 
Fat 


13 
mos. 
old 
Fat 


18 

mos. 
old 
Fat 


Average 
of All 


Water 

Insoluble protein 
Soluble protein . . 
Meat extractives . . 
Ash 


79-41 

15-85 

1.29 

2.18 

1.27 


79.02 

15-73 

i-93 

2.17 

I.I5 


81.01 

14.89 

1.56 

1.44 

1. 10 


80.35 

15.12 

1.72 

1.74 
1.07 


79-35 

15-74 

1.63 

2.14 

1. 14 


78.60 

i5-9o 
1.90 

2.40 
1.20 


80.21 

14.86 

2.16 

1.66 

1. 11 


79.17 

15-65 

2.16 

1.84 

1.18 


79.64 
15-47 -I 

1.79 W9-2I 

1-95 J 

11S 




100.00 


100.00 


100.00 


100.00 


100.00 


100.00 


IOO. CO 


100.00 


100.00 



1 Jour. Landw., 26 (1878), 549; 28 (il 

2 Maine Expt. Sta. Rpt. 1895, H, 36. 



5i), 289. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 53 
Table 8. — Average Composition of Fat-free Lean Meat of Steers 



Water 

Total nitrogenous matter (by 

difference) 

Ash ... 



22 Mos. Old 



No. 1 



77.61 

21.37 
1.02 



100.00 



No. 4 



76.60 

22.30 
1. 10 



32 Mos. Old 



No. 2 



78.01 

20.94 
1.05 



100.00 



No. 3 



77.18 

21.77 
1. 05 



100.00 



Average 
of All 



77-35 

21.60 
1.05 



100.00 



The figures of the foregoing tables indicate but very slight 
differences in the composition of the fat-free lean meat of the 
different animals, aside from a slightly greater water content 
in that of the sheep. An approximate average is 95 per cent total 
nitrogenous matter and 5 per cent ash in the dry, fat-free sub- 
stance. 

£n the course of investigations upon human nutrition, nu- 
merous analyses have been made of the various commercial cuts 
of meat which in general confirm the foregoing figures and 
show relatively small differences in this respect between the 
different cuts. 

88. Elementary composition of fat-free meat. — The fol- 
lowing analyses by Rubner, Stohmann and Langbein, and Ar- 
gutinsky show the ultimate composition of ash-free muscular 
tissue after prolonged extraction with ether : — 

Table 9. — Composition of Fat- and Ash-free Muscular Tissue 



Rubner 

Stohmann and Langbein 
Argutinsky .... 



Carbon 

% 



53-40 
52.02 

52-33 



Hydro- 
gen 

% 



7-30 
7-30 



Nitro- 
gen 

% 



16.30 
16.36 
16.15 



Oxygen 

% 



24.32 
24.22 



Heat of 

Combustion 

per Gram. 

Cals. 



5.6561 
5.6409 



Kohler x has investigated the elementary composition of the 
muscular tissue of cattle, sheep, swine, horses, rabbits and 
hens. The material was prepared with much care, the fat being 

1 Ztschr. Physiol. Chem., 31 (1901), 479. 



54 



NUTRITION OF FARM ANIMALS 



removed as fully as possible by prolonged extraction with 
ether. The residual fat which cannot be removed in this way 
was determined by Dornmeyer's digestion method and a cor- 
responding correction made in the analytical results. The fol- 
lowing are his averages for the fat- and ash-free substance : — 

Table io. — Composition of Fat- and Ash-free Lean Meat 



Heat of 
Combus- 
tion per 
Gram. 
Cals. 



Cattle 

Sheep 

Swine 

Horse 

Rabbit 

Hen 



No. 
of Sam- 
ples 


Carbon 

% 


Hydro- 
gen 

% 


Nitro- 
gen 

% 


Sulphur 

% 


Oxygen 

% 


4 


52-54 


7.14 


16.67 


0.52 


23.12 


2 


52-53 


7.19 


16.64 


0.69 


22.96 


2 


52.71 


7.17 


16.60 


o.59 


22.95 


3 


52.64 


7.10 


15-55 


0.64 


24.08 


2 


52.83 


7.10 


16.90 


— 


— 


2 


52.36 


6.99 


16.88 


0.50 


23.28 



5.6776 
5-6387 
5-6758 

5-5990 
5.6166 

5-6173 



All the samples were tested for glycogen, but only traces 
were found, except in the horseflesh, for the two samples of 
which an average of 3.65 per cent was obtained, a result which 
accounts for the low figure for nitrogen. 



The tissues of alimentation 

89. Definition. — Under this heading may be grouped the 
organs and tissues directly concerned with supplying food to 
the organism, with its distribution through the body, and with 
the removal of waste products of cell activity. That is, it in- 
cludes the organs of digestion, resorption, circulation, respira- 
tion and excretion, which constitute what are ordinarily spoken 
of as the entrails of slaughtered animals. So far as most of the 
familiar internal organs of the animal are concerned they may 
be considered as made up to a large extent of the classes of tis- 
sues already considered. In addition, however, the internal 
organs include a somewhat distinct type of tissue, viz., glandu- 
lar tissue, which plays an especially important part in the di- 
gestive processes, while it is also of the highest significance for 
other bodily functions. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 55 

Glands, like many other organs, have as their basis a rather loose 
and soft framework of connective tissue serving to support cells 
whose function it is to prepare certain fluids or chemical substances 
required in the body. The largest gland is the liver, which secretes 
the bile and has other important functions. Other examples are the 
pancreas, spleen, salivary glands, etc. Less conspicuous but equally 
important are the smaller glands imbedded in the walls of the stomach 
and intestines which secrete such important fluids as the gastric 
juice, intestinal juices, etc. 

90. Chemical composition. — From the standpoint of hu- 
man nutrition, the tissues of alimentation of farm animals, as 
here broadly defined, are largely waste products. While cer- 
tain organs, like the liver, kidneys, heart, etc., are utilized as 
food, the larger portion of the entrails passes into the offal and 
the feed consumed in its growth and maintenance is a part of 
the necessary cost of production of animal foods. 

An idea of the composition of the offal and of the proportion 
of total protein, fat and ash of the body which it contains is 
afforded by Lawes and Gilbert's analyses of entire animals (97), 
although the offal in their experiments included, in the case of 
cattle and sheep (but not of pigs), the head, feet and skin, while 
the kidneys and kidney fat were in all cases included in the 
carcass. On the average of the ten animals the percentage 
composition of the carcass and of the offal was : — 

Table ii. — Composition of Carcass and Offal 



In the fresh state 

Water 

Ash . 

Nitrogenous matter . 
Fat 

In the fat-free dry matter 

Ash 

Nitrogenous matter . 



Carcass 

% 



48.4 

3-7 

13-5 

34-4 



100. o 

21.5 

73-5 
100. o 



Offal 

% 



58.8 

17.2 
21.0 



100. o 

14.9 
85.1 



56 



NUTRITION OF FARM ANIMALS 



Table 12. — Percentage Distribution of Ash, Protein and Fat 
between Carcass and Offal 



Fat calf 
In carcass 
In offal . . 

Half -fat ox 
In carcass 
In offal . . 

Fat ox 
In carcass 
In offal . . 

Fat lamb 
In carcass 
In offal . . 

Store sheep 
In carcass 
In offal . . 

Half-fat old sheep 
In carcass 
In offal . . 

Fat sheep 
In carcass 
In offal . . 

Extra-fat sheep 
In carcass 
In offal . . 

Store pig 
In carcass 
In offal . . 

Fat pig 
In carcass 
In offal . . 

Mean of all 
In carcass 
In offal . . 



Ash 



100. o 



Protein 

(NX 6.25) 



73-2 
26.8 


65-9 

34-i 


70.5 
29-5 


100.0 


100.0 


100.0 


77-3 
22.7 


66.8 
33-2 


78.1 

21.9 


100.0 


100.0 


100.0 


77.0 
23.0 


67.2 

32.8 


77.0 
23.0 


IOO. 


100.0 


100.0 


74.0 

26.0 


52.1 

47-9 


78.1 

21.9 


100.0 


100.0 


100.0 


73-5 
26.5 


52.8 

47.2 


67.2 

32.8 


100.0 


100.0 


100.0 


69.8 
30.2 

100.0 


54-3 

45-7 

100.0 


72.0 

28.0 


1 00.0 


70.5 

29-5 


52.5 

47-5 


73-5 
26.5 


100.0 


100.0 


100.0 


60.2 
39-8' 


50.0 
50.0 


75-9 
24.1 


1 00.0 


100.0 


100.0 


64.0 
36.0 


69.4 

30.6 


80.3 

19.7 


100.0 


100.0 


100.0 


64.4 

35-6 


74.0 

26.0 


89-3 

10.7 


100.0 


1 00.0 


100.0 


71.4 
28.6 


60.8 

39-2 


77.2 

22.8 



100.0 



Fat 



1 00.0 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 57 

It thus appears that the offal contained relatively more pro- 
tein and water and less ash and fat than the carcass. From the 
weights of the carcass and offal, respectively, may be computed 
the percentage distribution of the ingredients between the two 
with the results shown in Table 12, from which it appears 
that on the average 39 per cent of the protein, 28 per cent of 
the ash and 23 per cent of the fat of the entire animal was 
contained in the offal. 

Epidermal tissues 

91. Functions. — The epidermis, or outer layer of the skin, 
consists of numerous layers of cells of which those nearer the 
true skin are alive and capable of multiplication while towards 
the outer surface they are gradually transformed to flattened, 
horny scales which serve as a protective layer and gradually 
slough off. Both the epidermis and the protective covering of 
animals, — hair, wool, feathers, etc., — as well as the hoofs 
and horns, corresponding to the nails in man, are modified forms 
of epidermal tissue, their characteristic ingredients being the 
class of albuminoids designated as keratins (51 e). 

92. Composition. — Except for their high and variable sul- 
phur content, the keratins differ little in elementary composi- 
tion from the simple proteins, but they are much more resistant 
to chemical reagents, being, for example, insoluble in alkalies in 
the cold and unattacked by either pepsin or trypsin. These 
properties fit them well for the outer covering of the animal. 
The following table shows the elementary composition of some 
of the more important epidermal tissues : — 

Table 13. — Composition of Epidermal Tissues 



Epidermis of man 
Hair . . . . 
Nails .... 
Horn of cow . . 
Hoof of horse 
Pure dry wool . 
Pure dry wool . 



Carbon 


Hydro- 


Nitro- 


Oxygen 


Sulphur 


% 


gen 
% 


gen 
% 


% 


% 


50.28 


6.76 


17.21 


25.01 


o.74 


50.65 


6.36 


17.14 


20.85 


5.00 


51.00 


6.94 


17-51 ' 


21-75 


2.80 


5I-03 


6.80 


16.24 


22.51 


3-42 


51-41 


6.96 


17.46 


19.49 


4-23 


49.67 


7.26 


16.01 


23-65 


3-4i 


49.89 


7-36 


16.08 


23.10 


3-57 



58 NUTRITION OF FARM ANIMALS 

The reserve tissues 

93. Food storage. — The classes of tissue considered in the 
foregoing paragraphs may be said in a general way to constitute 
the working machinery of the body. They are composed of 
cells which either serve the organism through specific activities 
of their protoplasm, as by producing motion of one sort or an- 
other, transmitting stimuli or secreting enzyms or other prod- 
ucts, or which, by means of the extraordinary development 
of their intercellular substance, support and protect the various 
organs of the body as a whole. 

As previously stated, however (77), many cells have the 
power of storing up surplus food in the form of cell enclosures, 
especially as fat or glycogen, which apparently constitute 
no part of the protoplasm itself but which are simply re- 
serve material. This is more or less true of all cells, but 
certain tissues show this property to a marked degree so that 
they may properly be spoken of as preeminently the reserve 
tissues. 

94. Adipose tissue. — The most familiar and most im- 
portant form of reserve tissue is adipose tissue, in which the 
stored material consists of fat and which constitutes the great 
store of reserve material in the animal body. 

Fat in the form of minute droplets may be deposited in the 
cytoplasm of all body cells but the presence of more than minute 

amounts in normal cells of muscles, 

•■.-.Nucleus. nerves, glands, etc., is unusual, 

ro op asm. -^ . g ^^ icularly in certain cells 

of the connective tissue that the 
• Fat drop. large accumulations of visible fat 

' Cell-membrane. m tne body take place. At the 
outset these cells present no special 
,-rFl G ' £ ~~. p c k e m e of a fat cell, characters, but in a well-nourished 

(Bohm, Davidorf, Huber, Text Book 

of Histology.) animal globules of fat begin to 

accumulate in them, the cells en- 
large, the globules of fat coalesce into larger ones and finally 
the cell substance is reduced to a mere envelope, cytoplasm 
and nucleus being pushed to one side and almost the whole 
volume of the cell occupied by fat. Masses of connective tissue 
thus loaded with fat constitute adipose tissue. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 59 




Fig. 6 



The increase of adipose tissue, according to Waters and Bell, 1 takes 
place in two ways : first by the formation of new cells and second by 
an increase in the size of existing cells as the storage of fat proceeds. 
They observed fat cells 
ranging from 20 fx in di- 
ameter in an emaciated 
animal to about 60 /x in an 
animal in ordinary thrifty 
condition and to as much 
as 200 ft in a very fat 
animal. The corresponding 
relative volumes, therefore, 
are 1 : 27 : 1000. 

There are two regions in 
particular in which fat tends 
to accumulate, viz., in the 
subcutaneous connective 
tissue and in the connective 
tissue surrounding the in- 
ternal organs, especially that 
of the mesentery and omen- 
tum, although all the looser 
forms of connective tissue, 
including, as already noted, 
the connective tissue lying 
between and within the 
muscles, may serve for the 
storage of fat. 

95. Composition of 
adipose tissue. — What is 
here called adipose tissue 
is commonly spoken of as 
fat, but it is evident that 
only a portion of it is fat 
in the strict sense, the re- 
mainder consisting of con- 
nective tissue, made up of 
albuminoids, or collagens, 
together with their ac- 
companying water. It is 




Fig. 




Fig. 8 



Figs. 6-8. — Successive stages in the forma- 
tion of adipose tissue. (Hough and Sedgwick, 
this nitrogenous material The Human Mechanism.) 



1 Proceedings, Soc. Prom. Agri. Science, 1909, pp. 20-24. 



6o 



NUTRITION OF FARM ANIMALS 



which forms the " cracklings " when the fat is melted out as in 
making lard or tallow. 

It is evident that the composition of adipose tissue must 
vary according to the extent to which the deposition of fat in the 
cells has been carried. When the cells are enlarged and well 
filled with fat, as in the fattened animal, the percentage of fat 
will be high and that of protein, water and ash correspondingly 
low. When there has been little deposition of fat, or when fat 
previously present has been withdrawn by starvation, the fat 
content will be low and the percentage .of protein, water and 
ash will be high. The following figures reported by Beythien for 
the extremes of composition of the adipose tissue of commercial 
beef, pork and mutton serve to give a general idea of the com- 
position of such deposits in well-fed animals. 

Table 14. — Range of Composition of Adipose Tissue of Commercial 

Meat 



Water . . . . . 

Fat 

Nitrogenous matter 
Ash 



Maximum 

% 




As an illustration of the variations in the composition of 
adipose tissue in different regions of the body the following 
average figures found by Henneberg, Kern and Wattenberg for 
the composition of the fat tissues of five lambs may be pre- 
sented. 

Table 15. — Composition of Adipose Tissue of Different Regions 



Water .... 

Fat 

Fat-free dry matter 



Subcuta- 
neous Fat 

% 



11.00 

84.49 

4-5i 

100.00 



Kidney 
Fat 

% 



4-36 

93-89 

i-75 

100.00 



Intestinal 
Fat 

% 



5.82 
92.15 

2.03 

100.00 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 6 1 

At the other extreme stand the figures reported by Trow- 
bridge x for the composition of the kidney fat of a steer which 
had received a submaintenance ration for about eleven months 
and was in a very reduced condition : — 

Water 81.42 per cent 

Protein 9.60 per cent 

Fat 4-59 P er cent 

96. Glycogen storage. — In addition to the large accumula- 
tions of fat which the body sometimes contains, a much more 
limited storage of reserve material may occur in the form of 
the carbohydrate glycogen, especially in the muscles and in the 
liver. 

Neumeister estimates that the liver of the average man may 
store up approximately 150 grams of glycogen and the muscles 
and other tissues approximately the same amount, making a 
total of about 300 grams for the entire body. Estimating the 
weight of the liver of a 1200 pound steer at 16 pounds and that 
of the muscles at 800 pounds, and assuming a content of 10 per 
cent of glycogen in the liver and one of 0,4 per cent in the mus- 
cles, the total amount of glycogen contained in the body would 
be approximately 2200 grams, but naturally this amount would 
vary greatly at different times according to the conditions of 
feeding and exercise. 

§ 3. The Composition of the Animal as a Whole 

97. Composition of entire body. — In view of the great num- 
ber of individual chemical compounds already discovered in 
the animal body and of the lack of accurate quantitative methods 
for the determination of many of them, any complete and de- 
tailed estimate of the composition of the body as a whole is 
manifestly impossible. The most that can be done is to de- 
termine the proportions of the principal groups of compounds 
enumerated in Chapter I. Several such investigations have 
been made at different times. In all of them water and dry 
matter, as well as the fat content of the latter, have been de- 
termined, while sometimes determinations of the total nitrogen 

1 Proc. Amer. Soc. Animal Nutrition, 1910, p. 13. 



62 



NUTRITION OF FARM ANIMALS 



or of the ash or of both have been added. From such investi- 
gations a general idea may be reached of what might be called 
the gross composition of the body. 

Table 16. — Composition of Entire Bodies of Animals — Empty 

Weight 





Spe- 


Age 


Condition 


Percentage Composition 






Pro- 
tein 




Dry 






cies 






Ash 


Fat 


Mat- 
ter 


Water 






C 9-10 wks. 
1 4 yrs. 
1 4 yrs. 


Fat 


3-9 


15-9 


15-3 


34-9 


65.1 




Cattle 


Half-fat 


5-o 


18.4 


20.8 


43-9 


56.1 






Fat 


4.2 


15-4 


32.0 


51-6 


48.4 






6 mos. 


Fat 


3-2 


13-4 


31-2 


47-8 


52.2 


Lawes and Gilbert 




1 yr. 


Store 


3-4 


15-8 


19.9 


39-o 


61.0 


Phil. Trans., Part ' 


Sheep 


3i yrs. 


Half-fat 


3-5 


15-5 


25-9 


44-8 


55-2 


II (1859), P- 493 




i\ yrs. 


Fat 


3-o 


13.0 


37-8 


53-8 


46.2 






if yrs. 


Extra fat 


3-1 


11.6 


48.3 


62.9 


37-1 






n-i2mos. 


Store 


2.8 


14.6 


24.6 


41-9 


58.I 




Swine 


\ n-nmos. 


Fat 


i-7 


11.4 


43-9 


57-o 


43 -o 






r 165 mos. 


— 


2.63 


12.71 


40.56 


56.11 


43-89 


Soxhlet 


Swine 


< 19 mos. 


— 


2.44 


12.92 


35-69 


5I-56 


48.44 


Centbl. Agr. Chem., 




1 19 mos. 


— 


2.17 


10.88 


44-59 


58.55 


41-45 


10 (1881), 674 • 




9 mos. 


Unfattened 


3-94 x 


22. 76* 


19.03 


45-73 


54-27 






9 mos. 


Unfattened 


3-861 


23. 24 2 


15.80 


42.90 


57-IO 






10 mos. 


Fattened 


3-2I 1 


19.01 2 


24.49 


46.71 


53-29 


B. Schulze 


Geese 


10 mos. 


Fattened 


3-59 1 


17.82* 


26.78 


48.19 


51-81 


Landw. Jahrb., 11 


10 mos. 


Fattened 


3-38 » 


19.19 « 


26.82 


49-39 


50.61 


(1882), 57 • • 




10 mos. 


Fattened 


3-41 1 


18.78* 


29.22 


5I-4I 


48.59 






10 mos. 


Fattened 


2.99 1 


18.53 ! 


25-36 


46.88 


53-12 






, 10 mos. 


Fattened 


3-i8i 


18.93 2 


26.21 


48.32 


51.68 






f 10 wks. 
9 wks. 


Unfattened 


3-Si 3 


14.30 4 


10.27 


28.08 


71.92 


Tschirwinsky 


Swine 


Unfattened 


4-I4 3 


15.21 4 


10.39 


29.74 


70.26 


Landw. Vers. Stat., 


| 28 wks. 


Fattened 


2.62 3 


11.08 4 


40.92 


54.62 


45-38 


29 (1883), 317 • 




1 23 wks. 


Fattened 


3-90 3 


11.70 4 


27.77 


43-37 


56.63 


Chaniewski 




■ Mature 


Thin 


3-35 


26.93 2 


6.65 


36.85 


6315 


Ztschr. Biol., 20 




Mature 


Fat 


3-19 


23-9° 2 


12.68 


39-67 


60.33 


(1884), 179 


Geese 


Mature 


Fat 


2.79 


21.742 


19.89 


44-36 


55-64 


(Computed on total 




Mature 


Fasted 


5- 11 1 


21.372 


3-26 


29.74 


70.26 


live weight) . . 




• Mature 


Fat 


3-94 l 


19.98 1 


16.01 


39-93 


60.07 


Jordan 




( 23 mos. 




4-45 


17-381 


18.80 


40.63 


59-37 


Maine Expt. Sta., 


Cattle 


I 23 mos. 




5-17 


17-51 x 


20.19 


42.87 


57-13 


Rept. 189s, II, 36 


1 33 mos. 




5-14 


16.59 1 


25.18 


46.91 


53-09 


(Hides not included) 




1 33 mos. 




5.24 


16.73 J 


24.62 


46.59 


53-41 











6.15 1 


12.19 


1 .31 


1965 


80.35 











6.36 1 


11.92 


1-55 


19.83 


80.17 


Wilson 


Swine 







6.361 


12.51 


1.60 


20.46 


79-54 


Amer. Jour. Physiol. 


16 days 




3.92 l 


U-57 


I.29 


19.78 


80.22 


8 (1903), 197 




16 days 




4-I5 1 


14-78 


1-43 


20.36 


79-64 






16 days 




4-561 


14-13 


1-35 


20.04 


79.96 



1 By difference. 

p By difference in soft parts. 



2 Includes feathers. 

4 By difference in bones. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 63 

The earliest investigation of this sort was that of Lawes and 
Gilbert 1 in 1859, already several times referred to, in which 
analyses were made of both the carcass and the offal parts of 
ten animals, viz., a fat calf, a half -fat ox, a moderately fat ox, 
a fat lamb, a store sheep, a half-fat sheep, a fat sheep, a very 
fat sheep, a store pig and a fat pig. The determinations made 
included total dry matter, ash, fat and total nitrogen. Several 
later investigators have also reported analyses of the entire 
bodies of animals, including cattle, swine and geese. 

Table 16 contains the results of these various investigations 
up to 1903 arranged chronologically. In all cases where the 
data given permit, the results have been computed upon the 
" empty " weight of the animals, that is, upon the live weight 
minus the contents of the digestive tract. On account of 
this recalculation, the figures for Lawes and Gilbert's results 
differ somewhat from those usually cited. In all cases where 
nitrogen was determined the " protein " equals N X 6.25. In 
those cases in which nitrogen was not determined the protein 
is equivalent to fat- and ash-free dry matter. 

Haecker, 2 as the result of analyses of the bodies of sixty well- 
fed steers, has reported the following average composition at 
various weights. 

Table 17. — Composition of Steers at Various Stages — Empty 

Weight 



Normal Weight 


Water 


Dry Matter 


Protein 


Fat 


Ash 


lbs. 


% 


% 


% 


% 


% 


100 


71.85 


28.15 


19.90 


3-99 


4.26 


200 


69.47 


30.53 


19.63 


6.26 


4.64 


300 


66.31 


33-69 


19-35 


9.84 


4-50 


400 


65.76 


34-24 


19-31 


10.56 


4-37 


500 


62.91 


37-09 


I9.I5 


13-73 


4.21 


600 


62.21 


37-79 


19.22 


13-97 


4.60 


700 


60.75 


39-25 


18.83 


15-91 


4-5i 


800 


57-88 


42.12 


18.69 


19.23 


4.20 


900 


54-09 


45-90 


17.66 


24.08 


4.16 


1000 


53-09 


46.91 


17-57 


25-53 


3.81 


1 100 


48.02 


51.98 


16.19 


31-91 


3-88 


1200 


48.64 


51-36 


15-66 


31.10 


3-67 



1 Phil. Trans., Part II, 1859, p. 493. 

2 Amer. Soc. Animal Produc, Proc, 1914, p. 18. 



6 4 



NUTRITION OF FARM ANIMALS 



It appears from the foregoing figures that the most abundant 
single constituent, although one which is subject to marked 
variations, is water, its percentage ranging from over 80 in 
very young pigs to 37 in a very fat sheep. Only in this latter 
case and two others does the percentage of water fall below 
that of fat. Relatively, the greatest variations are in the fat, 
as would be expected, since fat is the reserve material of the 

Table 18. — Composition of Fat-free Body — Empty Weight 





Live 
Weight 


Age 


Ash 


Pro- 
tein 


Dry 

Matter 


Water 




Lbs. 




% 


% t 


% 


% 


Cattle 














Lawes and Gilbert . 


— 


9-10 wks. 


4.60 


18.80 


23.10 


76.90 




— 


23-33 mos. 


6.45 


21.92 


28.37 


71.63 


Lawes and Gilbert . 


— 


4yrs. 


6.30 


23.20 


29.00 


71.00 




100 




4.44 


20.73 


25-17 


74.83 




200 




4-95 


20.94 


25.89 


74.11 




300 




4.99 


21.46 


26.45 


73-55 




400 




4.89 


21.59 


26.48 


73-52 




500 




4.88 


22.20 


27.08 


72.92 


Haecker .... 


600 




5-35 


22.34 


27.69 


72.31 




700 




5.36 


22.39 


27.76 


72.24 




800 




5.20 


23.14 


28.34 


71.66 




900 




5-48 


23.76 


28.74 


71.26 




1000 




5.12 


23-59 


28.71 


71.29 




1 100 




5-7o 


23.78 


29.48 


70.52 




. 1200 




5-33 


24.08 


29.41 


7o.59 


Sheep 














Lawes and Gilbert . 


— 


6 mos. 


4.60 


19.60 


24.10 


75-9o 


Lawes and Gilbert . 


— 


1-2 yrs. 


5.00 


21.20 


25.90 


74.10 


Lawes and Gilbert . 


— 


3i yrs. 


4.70 


21.10 


25-50 


74-50 


Swine 




1 










Wilson .... 


— 


New born 


6.38 


12.39 


18.77 


81.23 


Wilson .... 


— 


16 days 


4.27 


14.69 


18.96 


81.04 


Tschirwinsky . . 


— 


9-10 wks. 


4.27 


16.45 


20.72 


79.28 


Tschirwinsky . . 


— 


23-28 wks. 


4.92 


17-47 


22.39 


77.61 


Lawes and Gilbert 


— 


11-12 mos. 


3-40 


19.90 


23.10 


76.90 


Soxhlet .... 


— 


17-19 mos. 


4.04 


20.37 


25-34 


74.66 


Geese 














B. Schulze . . . 


— 


9-10 mos. 


4-54 


26.06 


30.60 


69.40 


Chaniewski . . . 


— 


Mature 


4.14 


25.85 29.93 


70.07 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 65 

body and may be stored up in large quantities, reaching in one 
instance 48 per cent, or, on the other hand, may be almost lack- 
ing in the insufficiently fed or fasted animal. 

98. Composition of fat-free body. — Since the adipose tissue 
of the animal body represents substantially a storage of reserve 
material (93, 94) temporarily set aside from the physiological 
activities of the organism, a better idea of the composition 
of the working machinery of the body is obtained by computing 
its composition fat-free as in Table 18. 

When this is done, it appears that the composition of the fat- 
free body is much less variable than that of the body as a whole, 
the chief difference being due to variations in the water content, 
which in turn depends chiefly upon the age of the animal, as 
the preceding table shows. So far as can be concluded from 
these few cases, however, the fat-free bodies of mature cattle 
would appear to contain three to four per cent less water than 
those of mature sheep or swine. In the case of geese, the per- 
centage of water is probably low on account of the relatively 
small amount in the feathers. 

99. Composition of fat- and ash-free dry matter. — In some of 
the foregoing investigations, viz., in Lawes and Gilbert's, Sox- 
hlet's and three of Chaniewski's, the total nitrogen was deter- 
mined and the protein has been calculated by multiplying by 
the factor 6.25. These experiments permit a computation of 
the percentage of nitrogen contained in the fat-free dry matter 
which in the other experiments has been regarded as protein. 
For example, in the case of Lawes and Gilbert's fat calf the figures 
are as follows : — 

Per cent 

Total dry matter 34.9 

Ash .......... 3.9 

Fat 1^3 19-2 

Fat- and ash-free dry matter . . . 15.7 
Total nitrogen 2.537 

2.537 -1- 15.7 = 16.16% nitrogen in ash- and fat-free dry 
matter. 

The results of such a computation for all of the experiments 
in which the published data permit it are contained in 
Table 19. 



66 



NUTRITION OF FARM ANIMALS 



Table 19. — Nitrogen in Fat- and Ash-free Dry Matter 



Lawes and Gilbert 



Soxhlet 



Chaniewski 



Fat calf 
Half-fat ox 
Fat ox 
Fat lamb 
Store sheep 
Half-fat sheep 
Fat sheep 
Extra-fat sheep 
Store pig 
Fat pig 

Average 

Swine 
Swine 
Swine 
Average 

Geese 
Geese 
Geese 
Average 



Empty 


Weight 


Fat- and 




Ash-free Dry 


Nitrogen 


Matter 




% 


% 


15-7 


2-537 


18.1 


2.950 


15-4 


2.466 


13-4 


2.150 


15-7 


2-525 


15-4 


2.486 


13.0 


2.085 


11.5 


1.857 


14-5 


2.342 


11.4 


1.830 


15-54 


2-033 


15-87 


2.068 


14.00 


1. 741 


26.84 


4-309 


23.80 


3.824 


21.68 


3-479 



Nitrogen 

in Fat- and 

Ash-free 

Dry 
Matter 

% 



16.16 
16.30 
16.01 
16.05 
16.08 
16.14 
16.04 
16.15 
16.15 
16.05 
16. II 

13.08 
I3-03 
12-44 
12.85 

16.06 
16.07 
16.05 
16.06 



With the exception of Soxhlet's experiments, the percentage 
of nitrogen approximates closely to that of animal proteins. 
If account be taken of the fact that the ether-extraction method 
used in these investigations does not completely remove the 
fat from dried animal tissue, the conclusion appears justified that 
the organic matter other than fat contained in the animal body 
has substantially the composition of protein. 



§ 4. The Composition of Feeding Stuffs 

100. Groups of ingredients. — As in the case of the animal 
body, the vast number of single chemical compounds found 
in the plant, as well as the lack of accurate quantitative methods 
for the determination of many of them, renders it practically 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 67 

necessary to be content in most cases with a separation of the 
plant substances into a few major groups or sub-groups of in- 
gredients. As ordinarily carried out, feeding stuffs analysis 
recognizes seven of these categories, viz., water, ash, protein, 
non-protein, ether extract, crude fiber and nitrogen-free ex- 
tract. 

101. Water. — The amount of water in a feeding stuff is 
commonly inferred from the loss of weight which the substance 
undergoes at a temperature above the boiling point of water. 
There is also a possibility, however, of a loss of other volatile 
matter besides water, while, on the other hand, some substances 
tend to absorb oxygen and thus increase in weight, especially 
when dried in air at a high temperature. The exact deter- 
mination of water and dry matter, therefore, is by no means an 
easy problem, but the results obtained by the ordinary methods 
are sufficiently exact for almost all purposes related to stock 
feeding. Commonly, the residue is weighed and regarded as 
dry matter, the amount of water being obtained by difference. 

102. Ash. — In the ordinary feeding stuffs analysis, ash is 
equivalent to the residue left after complete incineration of the 
substance in air or oxygen, the process being carried out at as 
low a temperature as practicable in order to avoid volatilization 
of part of the alkalies present. 

That this method fails entirely to distinguish between those ele- 
ments which were originally present as electrolytes and those which 
were in organic combination has already been pointed out (5), as has 
also the fact that certain elements, notably sulphur and phosphorus, 
are only partially recovered in the ash by the ordinary method of 
preparation. As the study of the functions of the ash ingredients pro- 
gresses, it may be anticipated that we shall come to determine the 
several elements involved in the way most appropriate to each rather 
than simply to determine the ash as a whole. 

103. Nitrogenous constituents. — As yet no methods exist 
for the quantitative separation of the nitrogenous constituents 
from the other ingredients of plants. While much labor has 
been expended upon a study of the individual proteins of a com- 
paratively few vegetable materials, and while in some instances 
it is possible to state with approximate accuracy the amounts 
of the several proteins present, nevertheless the only available 
methods for the determination of the nitrogenous compounds 



68 NUTRITION OF FARM ANIMALS 

of feeding stuffs in general are indirect ones based upon a 
determination of their characteristic element nitrogen. 

104. Crude protein. — In the method of feeding stuffs anal- 
ysis inherited from the early investigations of Henneberg and 
Stohmann, the protein is estimated from the amount of total 
nitrogen upon two assumptions: first, that all the proteins 
contain 16 per cent of nitrogen and, second, that all the nitro- 
gen of feeding stuffs exists in the protein form. On the basis 
of these assumptions, the protein is, of course, equal to total 
nitrogen multiplied by 6.25. The protein as thus determined 
is designated as crude protein to indicate the approximate na- 
ture of the determination. 

Subsequent investigations by Scheibler, E. Schulze, Kellner 
and others have shown the presence in many feeding stuffs 
of relatively large amounts of non-protein nitrogenous com- 
pounds, so that it is desirable to distinguish at least between the 
nitrogen present as true protein and that present in the simpler 
compounds grouped under the general term non-protein 
(60-67) , and all analyses of feeding stuffs for scientific purposes 
should at least make this distinction. Logically, too, the term 
crude protein should be dropped altogether, but when, as in 
the case of the older analyses, this is impracticable, care should 
be taken to retain the adjective, reserving the term " protein " 
for use in the sense given it in the next paragraph. 

105. True protein. — As a means of effecting an approximate 
separation of the true protein from the other nitrogenous 
compounds present in plants, advantage is taken of the fact 
that most of the latter class of substances are soluble in water. 
An aqueous extract of a feeding stuff, therefore, contains 
by far the larger share of its non-protein. Such an extract, 
however, contains also any water-soluble proteins existing 
in the substance. These are removed in part by coagulation by 
heating, i.e., by boiling the solution, and in part by the addition 
of some reagent with which they form insoluble compounds. 
Various substances have been used for this purpose but the 
present official method of analysis, based upon Stutzer's inves- 
tigations, uses copper hydrate as the precipitant. In practice, 
the feeding stuff is boiled with water, the precipitant added 
and the soluble matter filtered off. The nitrogen of the in- 
soluble residue is regarded as being protein nitrogen and from 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 69 

it by multiplication by 6.25 (or some other agreed factor) the 
amount of protein is calculated. 

It is obvious that this method of determining protein is sub- 
stantially a conventional method and that the adjective true 
is employed in a somewhat Pickwickian sense. The result 
probably includes all of the proteins of the feed but may also 
include other insoluble nitrogenous compounds. 

106. Non-protein. — The non-protein in feeding stuffs analy- 
sis includes all the nitrogenous compounds which remain in 
solution when the material is treated in the manner just de- 
scribed for the determination of protein. The nitrogen may 
be determined in the solution but ordinarily it is obtained by 
subtracting the protein nitrogen from the total nitrogen. The 
difference, multiplied by some conventional factor, equals the 
non-protein. Obviously, the non-protein is a heterogeneous 
mixture, varying as between different feeding stuffs and even 
in the same feeding stuff grown or harvested under different 
conditions. 

107. Nitrogen factors. — Evidently the accuracy with which 
the protein and the non-protein in a feeding stuff are determined 
depends not only upon the accuracy with which the protein 
and non-protein nitrogen can be separated and determined but 
also on the correctness of the factors used for converting nitro- 
gen into protein or non-protein respectively. 

For protein the usual factor has been 6.25 as already stated, 
based upon the assumption of 16 per cent of nitrogen in average 
protein. As was stated in Chapter I (44), however, different 
proteins vary in their nitrogen content, and in particular the 
vegetable proteins run higher in nitrogen than the animal pro- 
teins, which is, of course, equivalent to a smaller conversion 
factor. But while it is easily shown that the present factor is 
incorrect in many cases, it is not so easy to find a substitute. 
There is a rather wide range in the nitrogen content of the 
individual vegetable proteins, while most feeding stuffs con- 
tain two or more proteins in unknown proportions. Moreover, 
the proteins of the majority of feeding stuffs, especially of the 
roughages, have not yet been separated and studied. 

Ritthausen x has suggested the use of the factor 5.7 for the 
majority of cereal grains and leguminous seeds, 5.5 for the oil 

1 Landw. Vers. Stat., 47 (1896), 391. 



70 NUTRITION OF FARM ANIMALS 

seeds and for lupines, and 6.0 for barley, maize, buckwheat, 
soybean, white bean, and rape and other brassicas. 

For various classes of human foods, Atwater and Bryant l have 
proposed the following factors for the computation of protein 
from protein nitrogen : — 

Animal foods 6.25 

Wheat, rye, barley and their manufactured products . . . . 5.70 
Maize, oats, buckwheat and rice, and their manufactured 

products 6.00 

Dried seeds of legumes 6.25 

Vegetables 5.65 

Fruits 5.80 

For feeding stuffs whose proteins have not yet been studied, 
there seems to be no reason for changing from the present 
usage. 

With the non-proteins the case is even more perplexing in 
view of the greater variety of substances included under this 
term and the ' wide range of their nitrogen content. The 
writer has used tentatively 4.7, the factor for asparagin (66), 
one of the most widely distributed substances of this class, but 
the choice of this factor is substantially arbitrary. 

108. Crude fat. Ether extract. — The methods for de- 
termining the fat content of feeds are based upon its extrac- 
tion by means of some solvent which dissolves as little as 
possible of the other ingredients. A variety of solvents has 
been used for this purpose, such as carbon disulphid, carbon 
tetrachlorid, petroleum ether and the like, but the one most 
commonly employed is ethyl ether, or the so-called " sulphuric " 
ether commonly used as an anaesthetic. 

All the various solvents used, however, remove other sub- 
stances besides neutral fats and fatty acids, including more or 
less of the more complex lipoids. In particular the ether ex- 
tract obtained from coarse fodders contains a variety of waxes, 
resins, etc., as well as the chlorophyl of the leaves, and a rela- 
tively small proportion of true fats. It is customary, there- 
fore, to designate the extracted material as " crude fat " or, 
since ether is the reagent ordinarily used, as " ether extract." 

1 Storrs (Conn.) Agr. Expt. Sta., Rpt., 12, 79. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 71 

If a different solvent is used, this should be specified in the state- 
ment of the analysis. 

109. Crude fiber. — The so-called crude fiber of feeding stuffs 
is determined by boiling them first with dilute acid and then 
with dilute alkali under strictly defined conditions of concen- 
tration and time, and washing the undissolved residue with 
alcohol and ether. The residue, after deducting the small 
amount of ash remaining in it, constitutes the crude fiber. 

Crude fiber as thus obtained contains most of the cellulose, 
lignin and cutin of the feeding stuff, along with more or less 
of the more difficultly soluble hemicelluloses, particularly those 
containing pentosans. The proportion of pentosans contained 
in the crude fiber naturally varies according to the nature of 
the feeding stuff. Tollens, l for example, obtained the fol- 
lowing figures for the crude fiber of meadow hay and of brewers' 
grains : — 



Meadow hay . 
Brewers' grains 



Pentosans in 
Crude Fiber 



16.89 
11. 61 



Per Cent of Total 

Pentosans or Feed 

Retained in Crude 

Fiber 



23-63 
8.56 



110. Nitrogen-free extract. — All the ingredients of feeding 
stuffs which are not included in the foregoing six categories, 
viz., water, ash, protein, non-protein, ether extract and crude 
fiber, are usually grouped together under the collective name of 
nitrogen-free extract. The significance of the name is evident. 
By definition the nitrogen-free extract includes all those non- 
nitrogenous organic constituents, other than fat, which are 
extracted from the feeding stuff in the process of determining 
the crude fiber. The amount of nitrogen-free extract in a 
feeding stuff is not ascertained by any process of direct deter- 
mination but simply by subtracting the sum of the other six 
groups from 100 per cent. Such a residual group naturally in- 
cludes a great variety of substances of very diverse nature, 2 

1 Jour. Landw., 45 (1897), 103. 

2 For an enumeration of the principal ingredients of the nitrogen-free extract, 
compare Tollens, Jour. Landw., 45 (1897), 295. 



72 NUTRITION OF FARM ANIMALS 

but as a rule the nitrogen-free extract consists to a considerable 
extent of carbohydrates of one sort or another. Indeed, it has 
sometimes been designated by the latter name, but the use of 
the word in this sense is misleading and undesirable. 

The nitrogen-free extract includes not only hexose but also 
pentose carbohydrates, these latter substances being, therefore, 
by the ordinary method of feeding stuffs analysis, divided be- 
tween the crude fiber and nitrogen-free extract. Some of 
these various carbohydrates can be determined separately with 
a reasonable degree of accuracy, while others, including unfor- 
tunately starch, can be determined only more or less approxi- 
mately. That the nitrogen-free extract is far from consisting 
exclusively of carbohydrates has been strikingly shown by 
Stone. 1 He determined the content of the various classes of 
carbohydrates in samples of wheat and maize as accurately as 
possible and found that the sum in both cases was considerably 
less than the amount of nitrogen-free extract as determined 
by the conventional method. Much greater differences in this 
respect have been shown to exist in roughages. 

111. Classes of feeding stuffs. — The composition and char- 
acteristics of the principal classes of feeding stuffs are considered 
in Chapter XV, but it seems desirable to anticipate that dis- 
cussion here to the extent of indicating the three major classes 
into which the feeding stuffs are commonly divided. This 
classification is based primarily on botanical characteristics 
with which, however, are associated corresponding differences 
in chemical composition. 

Concentrates or concentrated feeds. — As the* name implies, 
these are feeding stuffs which contain much nutriment in a 
small bulk. They include primarily the grains and other seeds 
and, secondarily, a wide range of technical by-products de- 
rived from them as well as certain by-products of animal origin. 
Chemically, they are characterized by their relatively low con- 
tent of crude fiber, ranging from practically zero in certa'in by- 
products to perhaps 10 or 12 per cent in grains having a con- 
siderable proportion of hulls, like oats or buckwheat, and in 
certain by-products. 

Coarse fodders or roughage. — Botanically, these consist of 
the vegetative organs of the plant, i. e., substantially of stalks 

1 Jour. Amer. Chem. Soc, 19 (1897), 183. 



COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 73 

and leaves. They include hay, straw and other forms of for- 
age either fresh, ensiled or dried. Chemically, they are char- 
acterized by their relatively high percentage of crude fiber, 
which, however, naturally varies within quite wide limits. 
As compared with the concentrates they are bulky feeds and 
contain a larger proportion of difficultly soluble ingredients. 

Roots and tubers. — These feeding stuffs contain a large per- 
centage of water, resembling in this respect the fresh or ensiled 
roughages. Their dry matter, on the other hand, resembles 
that of the concentrates in containing relatively little crude 
fiber and a large proportion of ingredients which are easily 
soluble. They might be briefly characterized as dilute con- 
centrates. 



PART II 
THE PROCESSES OF NUTRITION 



CHAPTER III 
DIGESTION AND RESORPTION 

112. The first step in nutrition. — The facts considered in 
Part I have served incidentally to show some particulars of 
those differences between the feed of herbivora and the animal 
body which it serves to nourish which are, in a general way, 
familiar to every one. The former contains many ingredients 
not found in the latter, and it is plain that, for example, sub- 
stances like starch and cellulose must undergo considerable 
modification before they can be used in the animal organism. 
One need not be a chemist, however, to reach this conclusion. 
A simple comparison of the feeds given farm animals with the 
products which they manufacture out of them convinces one 
that profound changes are necessary to convert hay and grain 
into meat or milk. The first step in this process is the diges- 
tion of the feed. In all but the lowest animals, special tissues 
are set apart for this work, together constituting the organs 
of digestion, or the alimentary canal with its appendages. 

§ i. The Organs of Digestion 

113. General plan. — The process of digestion is seen in its 
simplest form in unicellular animals like the ameba. When 
the ameba comes in contact with a particle of feed, a depres- 
sion forms in its outer surface which finally closes around the 
particle, forming a cavity which serves as a temporary digestive 
organ. Undigested residues are rejected by the reverse pro- 
cess. In animals slightly higher in the scale, this temporary 
cavity becomes a permanent one, the same opening serving for 
the entrance of feed and the exit of waste. The next step in 
the evolution is the provision of a separate exit for the waste 
matter, thus giving the typical form of digestive apparatus, 
of which that of the higher animals is a development, consisting 

77 



78 NUTRITION OF FARM ANIMALS 

of a cavity or cavities communicating with the external world 
by two openings, one for the reception of feed and the other 
for the rejection of waste. In domestic animals, the digestive 
tract is large and of very complex structure, but in all cases it 
is built upon the general plan just outlined. Always, from the 
ameba up to man, the inner surface of the digestive cavity is 
morphologically simply a continuation of the external surface 
of the body, turned in as one might a glove finger. Conse- 
quently, the material contained in the digestive cavity, strictly 
speaking, is still outside the body. 1 

Finally, as an essential part of the digestive apparatus, there 
must be such organs as the cilia, tentacles, proboscis, lips, etc., 
by which feed is grasped and introduced into the digestive cavity, 
and likewise means by which it may be mechanically ground 
to fit it for the process of digestion, as, for example, the teeth 
of mammals, the bills and gizzards of birds, etc. 

For the present purpose, it is unnecessary to enter into any 
elaborate consideration of the anatomy of the digestive organs, 
since we are concerned chiefly with the chemical rather than 
the physical processes of digestion, and this section may be 
confined to a very general description of the digestive organs 
of domestic animals. In these animals, the digestive apparatus 
may be described briefly as a tube having various enlargements, 
folds and diverticula. 

114. Digestive fluids and enzyms. — In the ameba, what- 
ever changes are effected in the substances which it takes as 
feed are accomplished by the cells of the introverted surface 
or by their secretions. As the digestive apparatus becomes 
more complicated, however, a division of cellular labor takes 
place and certain groups of cells are set apart to produce the 
digestive juices which act upon the feed. In the higher animals, 
these cells become the numerous secreting glands which are 
an essential part of the organs of digestion. The principal 
active agents in digestion are certain enzyms secreted by these 
glands, the more important digestive enzyms in the higher 
animals being : — 

i. The amylases, ptyalin (in the saliva) and amylopsin (in 
the pancreatic juice), acting upon starch. 

1 For a more complete discussion of the development of the digestive apparatus 
see R. Meade Smith, The Physiology of the Domestic Animals, pp. 203-226. 



DIGESTION AND RESORPTION 79 

2. The invertases, sucrase, maltase and lactase (in the in- 
testinal juice), acting upon di-saccharids. 

3. The proteases, pepsin (in the gastric juice), trypsin (in 
the pancreatic juice) and erepsin (in the intestinal juice), act- 
ing upon proteins. 

4. The lipase, steapsin (in the pancreatic juice), acting upon 
the lipoids, or specifically the fats. 

115. The mouth. — The mouth is the organ of prehension 
and mastication. Chiefly by means of the tongue, lips and 
teeth, feed is seized and introduced into the digestive cavity, 
while the teeth serve also to grind it up, rendering it capable 
of being swallowed and also exposing more surface to the action 
of the digestive fluids. The mouth also receives the secretion 
of three pairs of glands called the salivary glands whose product 
is known as the saliva. These three pairs are called, respec- 
tively, the parotid, the submaxillary and the sublingual glands. 

The mixed saliva, consisting of the secretion of all three pairs 
of salivary glands, together with the comparatively insignificant 
amounts secreted by the various smaller glands of the mouth, 
is a thin, colorless, watery, slightly viscid liquid of alkaline 
reaction. The organic matter of the saliva includes a trace of 
albumin, more or less mucus, and the enzym ptyalin, 1 which 
is its active constituent. 

The saliva has both physical and chemical functions. The 
presence of feed in the mouth, its taste, odor or sometimes even 
sight, causes active secretion of saliva, which is mixed with the 
feed in the act of mastication and moistens and lubricates it 
so that it can be swallowed. With dry feeding stuffs, the 
amount of saliva required for this purpose is very large. The 
total secretion has been estimated at about 84 pounds per day for 
the horse and at least 112 pounds per day for the ox, although 
varying greatly with the dryness of the feed. Besides moisten- 
ing and lubricating the feed, the saliva has also a chemical action 
upon it. In a slightly alkaline medium and at body tempera- 
ture, the ptyalin acts upon the starch of the feed, converting 
it ultimately into maltose. 

116. The stomach. — From the mouth, the feed in the act 
of swallowing passes through the esophagus, or gullet, to the 
stomach which, except in fowls, is the first enlargement of the 

1 Not present in the saliva of carnivora. 



8o 



NUTRITION OF FARM ANIMALS 



alimentary canal. The horse and hog, as well as carnivorous 
animals like the dog and cat, have a single stomach cavity, 
while ruminants, such as cattle, sheep and goats, have a so- 
called compound stomach consisting, in the farm animals, of 
four divisions, called respectively the rumen, or paunch, the 




Fig. 9. — Sheep's stomach. (Hagemann, Anatomie und Physiologie der 

Haus-Saugetiere.) 

I, Rumen. 2, Reticulum. 3, Omasum. 4, Abomasum. 5, Duodenum. 6, Esophagus. 



reticulum, the omasum, or manifolds, and the abomasum, or 
true stomach. 

In reality the first three divisions of the ruminant stomach 
are to be regarded as dilatations of the esophagus in which the 
feed undergoes a softening and fermentation preliminary to 
true gastric digestion, while only the fourth division is a stomach 
in the strict sense. In domestic fowls a similar dilatation of 
the esophagus at the base of the neck constitutes the crop. 

Moreover, even the so-called single stomachs of the horse 
and hog, while they have but a single cavity, are in reality 
compound stomachs. In the case of the horse three quite 
distinct parts may be distinguished, viz., the left or cardiac 
portion, the fundus region and the pyloric region, the two latter 
having the functions of the true stomach. In the case of the 



DIGESTION AND RESORPTION 



8l 




Fig. io. — Stomach and duodenum of horse. (Hagemann, Anatomie und 
Physiologie der Haus-Saugetiere.) 

Sch., Esophagus. C, Cardiac portion. M, Fundus. F, Pyloric region. D, Duodenum. 



hog the cardiac portion is comparatively small and the remainder 
of the organ is to be regarded as constituting the stomach 
proper. 

117. Rumination. — In the ruminant, water and liquid 
feeds may pass quite 
directly to the aboma- 
sum, although as a 
matter of fact, they 

seem to reach all four x o 

divisions of the stomach. 
The more bulky feeds, 
however, fail to pass 
through the esophageal 
canal but enter the 
rumen and reticulum. 
This is especially the 
case because the rumi- 
nant masticates its feed FlG - ". — Stomach of hog. (Hagemann, Ana- 
very imperfectly at the 
time of eating. In the 
reticulum and especially 
in the capacious rumen, the partially masticated feed re- 
mains for some time in contact with the saliva and such 




1-4, Fundus. 2, Cardiac portion. 5, Pylorus. 
8, Duodenum. 



82 NUTRITION OF FARM ANIMALS 

portion of the drink as reaches this stomach and is thoroughly 
softened and prepared for further action. The rumen is 
so large that it always contains a considerable amount of 
material and the new feed when swallowed is more or less 
completely mixed with that already in the rumen by the peri- 
staltic action of the latter, thus tending to prolong its stay. 
The liquid or finely cohiminuted portions probably pass on 
directly to the omasum, or manifolds, and the abomasum, but 
the bulk of the feed undergoes the process of rumination. 

After the animal has completed feeding, and if it is left in 
quiet, small portions of the feed are raised again to the mouth 
from the rumen and reticulum by contraction of these organs, 
aided by the action of the abdominal muscles and of the dia- 
phragm, thoroughly chewed and swallowed a second time. 
This time they pass to a considerable extent, though not 
entirely, the esophageal canal and enter the third stomach, 
the manifolds, and from this pass into the fourth or true 
stomach. 

The ruminants are animals which in the wild state depend 
on speed and cunning to escape from their enemies. Hence 
it is an advantage to them to be able to consume hastily large 
amounts of feed and then to retire to some safe concealment 
to remasticate and prepare it for digestion. Rumination 
also enables these animals to utilize more thoroughly coarse 
rough fodders, the long stay in the paunch softening and fer- 
menting the material and helping especially to destroy or dis- 
solve the carbohydrates of the cell walls and thus render the 
cell contents accessible to the digestive fluids. 

118. The gastric juice. — The mucous membrane lining the 
true stomach contains numerous simple glands (tubular glands) 
differing in appearance in different portions of the stomach. 
Those of the fundus region contain two kinds of secreting cells, 
commonly designated as " chief " and " parietal " cells. The 
glands of the pyloric end contain " chief " cells similar to those 
of the fundus glands, but only an occasional " parietal " 
cell. The parietal cells secrete as their essential product 
hydrochloric acid. The " chief " cells produce the enzym 
pepsin, or rather a precursor of pepsin called pepsinogen. 
The mixed secretion of these different glands constitutes the 
gastric juice, which is a thin, clear acid liquid having a 



DIGESTION AND RESORPTION 83 

specific gravity of 1.005 to 1.01 and containing a maximum of 
about 2.5 per cent of solids. The combined action of the pepsin 
and hydrochloric acid of the gastric juice splits the proteins 
of the feed into derived proteins, especially proteoses and 
peptones, and to some extent into polypeptids. 1 The hydro- 
chloric acid of the gastric juice has also an important anti- 
septic action and likewise serves to dissolve more or less of 
the ash of the feed. 

In addition to its digestive action on proteins, the gastric 
juice contains an enzym which brings about the coagulation 
of the caseinogen of milk — the rennet ferment, or chymosin. 
According to some investigators, chymosin is identical with 
pepsin, but the weight of opinion seems to be in favor of its 
independent existence. 

119. The passage of feed from the stomach. — The lower 
or posterior end of the stomach is closed by a sphincter muscle 
called the pylorus, which prevents the ingested feed from pass- 
ing into the next division of the alimentary canal, the duodenum, 
or being forced into it by the contractions of the stomach. 
When in the course of gastric digestion, however, the difference 
between the acid reaction of the stomach contents and the al- 
kaline reaction which normally prevails in the duodenum 
reaches a certain level, the pylorus relaxes and allows the per- 
istaltic contraction of the stomach to press a portion of its acid 
contents into the duodenum. The partial neutralization of 
the duodenal contents which results causes the pylorus to close 
again until the alkaline reaction is restored, when the cycle may 
be repeated. 

The mechanism of this process has been especially studied by 
Cannon in carnivora, but it may be presumed that what is true of these 
animals is also substantially true of herbivora, although experimental 
proof of this is lacking. 

While both protein and carbohydrates undergo considerable 
digestion in the stomach, it is evident that one important 
function which the stomach performs is that of a receptacle 
which prevents too rapid passage of the feed into the duodenum 
and at the same time initiates chemical changes and prepares 

1 By prolonged peptic digestion in vitro amino acids may also be produced but 
it is not believed that this occurs in natural digestion. 



84 



NUTRITION OF FARM ANIMALS 



the feed for the more vigorous action of the intestinal enzyms. 
Moreover, the setting free of cell contents by the fermentation 
of the cell walls of vegetable feeds, as well as the liberation of 
the fat of animal feeds by the solution of the protein of the 
adipose tissue, render these materials more accessible to the 
action of the digestive juices. 

120. The small intestine. — On leaving the stomach through 
the pylorus, the feed enters the small intestine, which may briefly 

d 




Fig. 12. — Intestines of cattle. (Leisering, Die Rindviehzucht.) 

be described as a long, comparatively narrow tube. Its average 
length is, according to Colin, about nine times that of the body 
in the horse, sixteen times in the ox and sheep and eleven times 
in the hog. It is suspended in the abdominal cavity by a re- 
flection of the peritoneum called the mesentery, and as shown 
in Fig. 12 is much convoluted. It is commonly subdivided into 
duodenum, jejunum and ileum. 

121. The coecum. — From the small intestine the contents of 
the digestive tract pass, through the ileo-ccecal valve, into the 
ccecum, which is a diverticulum of the digestive canal, the point 



DIGESTION AND RESORPTION 



85 



of entrance from the small intestine and that of exit into the 
colon being near together and in the upper part of the ccecum. 
Anatomically, it might almost be called a second stomach. 
Its functions, however, resemble those of the first stomach of 
ruminants and not 
those of the true 
stomach, the feed 
stagnating, so to 
speak, in the 
ccecum and under- 
going extensive f er- 
mentation and 
putrefaction. The 
size of the ccecum, 
in a general way, 
varies inversely as 
that of the stom- 
ach. Thus in the 
horse it is very 
large, having about 
16 per cent of the 
total capacity of 
the digestive canal. 
In the ox, on the 
other hand, it has 
only about 3 per 
cent and in the 
sheep less than 2.5 
per cent of the total 
capacity and in the 
hog about 5.5 per 
cent. 

122. The large 
intestine. — The 
alimentary canal is 
continued from the 

ccecum as the large intestine, which, as its name implies, is gen- 
erally of greater diameter than the small intestine but also 
shorter. It is subdivided into the colon and the rectum and 
serves rather as a resorbent than as a digestive organ. The colon 




Fig. 13. — Coecum of horse. (Colin, Physiologie 
comparee des Animaux.) 



86 NUTRITION OF FARM ANIMALS 

is enormously developed in the horse, having about 45 per cent 
of the total capacity of the digestive tract, and serves, like the 
ccecum, to continue the digestion of the less soluble portions 
of the feed. 

123. The pancreas. — In the stomach, the glands which 
secrete the gastric juice are located in the mucous lining of the 
organ. In the case of the intestines, the glands which supply 
the various digestive juices, like the salivary glands of the mouth, 
lie in part entirely outside the alimentary canal proper. One 
of the most important of these is the pancreas. This is a large 
gland located near the stomach, liver and duodenum, its duct 
opening into the latter either by a common exit with that of the 
bile duct (horse, sheep), or somewhat lower down (cattle, swine). 
The secretory action of the pancreas, like that of the salivary 
and gastric glands, is intermittent, the gland being active only 
when feed is present in the duodenum. 

The pancreatic juice is a clear, viscid liquid, having an al- 
kaline reaction due to its content of sodium salts. It contains 
in the neighborhood of eight to ten per cent of solid matter and 
has a specific gravity of approximately 1.030. It differs from 
other digestive juices in containing a relatively large amount 
of protein. As in the case of all the other digestive fluids, the 
essential active ingredients are enzyms, of which the pancreatic 
juice contains three in particular, viz., a protease, trypsin, acting 
upon the proteins, an amylase, amylopsin, acting upon starch, 
and a lipase, steapsin, acting upon fats. Small amounts of 
chymosin and of a lactase have also been found. In the juice 
as secreted by the pancreas, the trypsin at least, if not the other 
enzyms, exists in the form of a pro-enzym, trypsinogen, which 
is converted into trypsin (" activated ") after the secretion 
reaches the duodenum. 

124. The liver. — This, the largest gland in the body, is 
located immediately below the diaphragm and lies chiefly on 
the right side of the body. It is relatively small in ruminants 
and large in the hog. 

The liver has other important functions in nutrition, as will 
appear in Chapter V, but as related to digestion it secretes the 
bile. This fluid, produced by the hepatic cells, passes from 
them into the bile capillaries, which unite to form small ducts, 
the latter finally coalescing and constituting the bile duct. In 



DIGESTION AND RESORPTION 87 

the horse, this empties directly into the duodenum a short 
distance from the stomach. In cattle, sheep and swine, the 
bile is stored up in the gall bladder, a reservoir from which a 
duct leads to the duodenum. 

The chief action of the bile is upon fats of the feed. To a 
small extent, it saponifies them and it also assists in emulsifying 
them. Its digestive action may, however, be more conveniently 
considered along with that of the pancreatic juice (126, 135). 
In addition to its action upon the fats, an antiseptic effect and 
also a stimulating effect upon peristalsis have been ascribed to 
the bile. 

125. The intestinal juice. — In addition to the external 
glands (pancreas and liver), already mentioned, the walls of 
the small intestine contain a large number of small glands of 
two kinds, Brunner's and Lieberkuhn's glands, which yield an 
intestinal juice containing a number of enzyms. Prominent 
among these are the invertases maltase, sucrase and lactase, 
which act upon the corresponding disaccharids, the maltose re- 
sulting from the digestion of starch being converted into dextrose, 
sucrose into a mixture of dextrose and levulose, and lactose, in 
suckling animals at least, into dextrose and galactose. 

There may also be extracted from the mucous membrane of 
the small intestine a protease called erepsin. This enzym does 
not act upon the native proteins, with the exception of casein, 
but acts powerfully upon the derived proteins (proteoses and 
peptones), hydrolyzing them and breaking them down very 
completely to their constituent amino acids. The presence of 
erepsin has also been demonstrated in the intestinal juice, but its 
action in this case was weaker than in the extracts of the intesti- 
nal wall and it may be that a portion of its action in the living 
animal takes place within the cells in which it is produced. 

The presence in the intestinal juice of an amylase, a lipase 
and of ferments (nucleinases and nucleotidases) , which act upon 
the nucleic acids has also been demonstrated. 

126. Intestinal digestion. — In the duodenum the neutraliza- 
tion of the acid material coming from the stomach is effected 
by the alkalies of the bile and pancreatic juice, while the bile 
also precipitates proteins and partly digested proteins in com- 
bination with the bile acids and this precipitate carries down 
with it mechanically the pepsin which is present. In these 



88 NUTRITION OF FARM ANIMALS 

two ways, namely by neutralization and precipitation, the pep- 
sin is prevented from digesting the enzyms of the pancreatic 
juice and bile, an action which would otherwise take place, since 
these enzyms appear to be substantially protein in their nature. 1 
In the small intestine, the neutralized contents of the stomach 
are subjected to the combined action of the pancreatic juice, 
the bile and the intestinal juice, while they are moved along 
through the successive divisions of the small and large intestines 
by means of the peristaltic movements of the latter. These 
movements serve also to mix the contents of the intestines 
and to bring them into intimate contact with the intestinal 
walls. . 

The fats of the feed, under the action of the steapsin of the 
pancreatic juice, undergo a cleavage into glycerol and fatty 
acids and this change is considerably accelerated by the bile, 
which also aids in emulsifying the fats and so exposing vastly 
more surface to the action of the enzyms. The fatty acids 
thus set free unite to a greater or less extent with the alkali of 
the pancreatic juice and bile, forming soaps, while both soaps 
and free fatty acids are soluble in bile in the presence of sodium 
carbonate. The presence of soaps in solution also aids, as was 
pointed out in Chapter I, in producing a permanent emulsion 
of the fats. 

Starch, if any escapes digestion in the stomach, is acted upon 
by the pancreatic amylopsin substantially in the same manner 
as by the ptyalin of the saliva but much more energetically, 
yielding maltose, while both maltose and any other disaccharid 
present in the feed are acted upon by the invertases of the in- 
testinal juice, yielding monosaccharids. 

Any proteins which escape digestion in the stomach, and 
likewise the proteoses and peptones resulting from peptic di- 
gestion, are hydrolyzed by trypsin and erepsin much more 
energetically than by pepsin and yield not only proteoses and 
peptones, but a whole series of progressively simpler poly- 
peptids and finally are largely or wholly split up into their 
constituent amino acids. 

1 The foregoing statements describe what takes place when the materials are 
mixed in the laboratory. The actual importance of the precipitation of the pepsin 
in the intestine is somewhat in doubt. 



DIGESTION AND RESORPTION 89 

§ 2. The Chemistry of Digestion 

127. Digestion a chemical process. — The foregoing para- 
graphs have dealt chiefly with those more general facts regard- 
ing the organs of digestion which are necessary for an under- 
standing of their functions and only incidentally and in outline 
with the chemical processes involved. It is now time to revert 
to the statement made at the beginning of the chapter, namely, 
that digestion is the first step in the conversion of feed sub- 
stances into body substances, and specifically in the case of farm 
animals the conversion of vegetable into animal substances. 
These, however, are chemical transformations and from this 
point of view a knowledge of the structure of the digestive 
apparatus is of significance chiefly as an aid to the understanding 
of these processes. In taking up this aspect of the subject, it 
will be convenient to consider the three chief groups of nutrients 
separately. 

The digestion of carbohydrates 

By far the larger proportion of the carbohydrates contained 
in the feed of farm animals consists of polysaccharids, especially 
starch, cellulose and the various pentosans and hexo-pentosans. 
The disaccharids, especially sucrose and lactose, probably stand 
next in importance, while comparatively small amounts of 
monosaccharids are consumed. 

128. Cellulose. — The cellulose of feeding stuffs was long 
assumed to be indigestible. Haubner was the first to show the 
incorrectness of this assumption and to prove that even the 
cellulose of such substances as paper pulp and sawdust, as well 
as that of ordinary feeds, was digested by cattle. The subse- 
quent investigations of Henneberg and Stohmann (158, 707) 
showed that the crude fiber of feeding stuffs was digested to a 
considerable extent by cattle and sheep, and later digestion ex- 
periments have proved this to be true not only of ruminants 
but to a varying degree of other animals, both herbivora and 
omnivora, including domestic fowls. Even man is capable of 
digesting the tenderer forms of cellulose to a considerable 
extent. 

None of the digestive enzyms of the higher animals, however, 
have been shown to have any action upon cellulose and the small 



90 NUTRITION OF FARM ANIMALS 

amounts of cellulose-dissolving enzyms (cytases) found in some 
feeds appear quite inadequate to account for its solution, so 
that the manner of its digestion was long a puzzle. The in- 
vestigations of Wildt l in 1874 upon the digestive process in 
sheep, however, showed, as Zuntz 2 subsequently pointed out, 
that the solution of cellulose occurs chiefly in those portions of 
the alimentary canal where the feed stagnates, — that is, in 
the paunch of the ruminant and in the ccecum and colon. 
This fact tended to confirm the view already advanced that the 
solution of cellulose in the digestive tract was due to a process of 
fermentation, and this hypothesis also served to explain the 
presence of methane and hydrogen in the digestive tract. Tap- 
peiner, 3 however, seems to have been the first to show ex- 
perimentally that the disappearance of cellulose in the digestive 
tract is effected by a fermentation brought about by the micro- 
organisms inhabiting the alimentary canal. 

Tappeiner's conclusions have been fully confirmed by more 
recent investigations, notably those of Markoff 4 in Zuntz's 
laboratory, while Kellner 5 has shown that the consumption of 
crude fiber (straw pulp) by cattle causes a marked increase in 
the amount of methane eliminated. In the light of these 
results it may be regarded as established that the disappearance 
of cellulose during its passage through the alimentary canal of 
herbivora is not due to a digestion in the sense of a simple hydro- 
lytic cleavage, like that of starch or protein, but to a destructive 
fermentation. The products of this fermentation are large quan- 
tities of carbon dioxid and methane and small amounts of hydro- 
gen, which are excreted, and various organic acids of the aliphatic 
series which combine with the alkalies of the saliva or other 
digestive fluids. The salts thus formed are resorbed and consti- 
tute the sole contribution which cellulose makes to the nutrition of 
the body. The principal acids formed appear to be acetic and 
butyric, although others are also present. In ruminants, the 
chief seat of this fermentation is the capacious first stomach, 
while in the horse, with his relatively small, simple stomach, 
it takes place principally or wholly in the enormous ccecum and 
colon. 

1 Jour. Landw., 22 (1874), 1. 2 Landw. Jahrb., 8 (1879), 101. 

3 Ztschr. Biol., 20 (1884), 52. 

4 Biochem. Ztschr., 34 (191 1), 211 ; 57 (1913), 1. 

5 Landw. Vers. Stat., 53 (1900), 193, 300. 



DIGESTION AND RESORPTION 91 

129. Pentosans. — The pentosans are widely distributed 
in the vegetable kingdom and appear to be contained chiefly 
or wholly in the cell walls of plants, probably in combination 
to a greater or less extent with hexosans. If the ordinary 
methods of feeding stuffs analysis are followed, both the crude 
fiber and nitrogen-free extract contain them (109, 110). 

Stone, 1 who was the first to show that they were digestible, 
found a percentage digestibility of about 60 for the pentosans 
in the ordinary feed of the rabbit. Later, 2 in conjunction with 
Jones, he showed that in 14 different samples of roughages 
from 48 to 90 per cent of the pentosans were digested by sheep, 
while in mixed rations the corresponding figures were from 46 
to 71 per cent. Weiske 3 about the same time obtained similar 
results in experiments with sheep and rabbits. The digesti- 
bility of pentosans has been fully confirmed by later experiments. 

But while pentosans are digestible, or at least disappear in 
the digestive tract, the manner of their digestion is not cer- 
tainly known. Up to the present time no enzyms have been 
discovered either in the digestive organs or elsewhere, which 
have been proved to be capable of hydrolyzing them. On the 
other hand, however, the pentosans are attacked by bacteria 
much like other carbohydrates and yield similar products, 
especially the acids of the aliphatic series. That the pentosans 
are to a considerable extent subject to the methane fermenta- 
tion in the digestive tract seems clear from Kellner's investi- 
gations upon straw pulp (128) , in which over one- third of the di- 
gested organic matter consisted of pentosans, so that it is difficult 
to resist the conclusion that these, as well as the cellulose, under- 
went fermentation. Moreover, in a large number of similar 
experiments, the methane fermentation has been found in a 
general way to be proportional to the total digestible crude 
fiber and nitrogen-free extract, including the pentosans. Of 
course these results do not preclude the possibility of a hy- 
drolysis of the pentosans in the digestive tract, converting them 
into pentose sugars, but as yet there is no direct evidence that 
such a process takes place. If it does not, then the products of 
the digestion of the pentosans are substantially the same as 
those from cellulose. 

1 Amer. Chem. Jour., 14 (1892), 9. 2 Agricultural Science, 7 (1893), 6. 

3 Ztschr. Physiol. Chem., 20 (1895), 489. 



92 NUTRITION OF FARM ANIMALS 

130. Hemicelluloses. — What is true specifically of the 
pentosans appears to hold also for the reserve carbohydrates 
of the cell wall — the so-called hemicelluloses (18) — as a 
whole. No animal enzyms are known which hydrolyze the 
galactans, levulans, etc., or which break up their union, if it 
exists, with the pentosans, but nevertheless these substances 
disappear in part in the digestive tract of herbivora. Pending 
more exact knowledge on this point, the assumption seems 
warranted that they as well as the pentosans undergo bacterial 
fermentation and yield substantially the same products. 

131. Starch. — The first agent to act upon starch is the 
ptyalin of the saliva (115). As is the case with the other 
enzyms, ptyalin has never been isolated, but its effects and the 
conditions governing its action have been extensively studied, 
in part owing to the ease with which saliva can be procured. 
The most important of these conditions are that ptyalin acts 
most efficiently in the neighborhood of 40 C, that is, at about 
blood temperature, in a neutral solution, while more than a 
trace of free acid or alkali inhibits its action. To acids or al- 
kalies combined with proteins, even though they show an acid 
or alkaline reaction to ordinary indicators, ptyalin is much less 
sensitive and it is also less sensitive to organic than to inorganic 
acids. In brief, the action of ptyalin is inhibited by a very low 
concentration of either hydrogen or hydroxyl ions. 

The action of ptyalin on starch consists of a succession of 
cleavages and hydrations resulting in the formation of the various 
dextrins (24) and finally of sugar. With cooked starch, the 
action is fairly rapid ; upon raw starch ptyalin acts more slowly, 
the rate varying somewhat with the kind of starch and being 
apparently determined by the degree of resistance of the cellulose 
envelope of the starch grains. Chemically, the action is analo- 
gous to that of acids, but is less vigorous and is not carried so far. 
The action of acids yields dextrose as a final product ; that of 
ptyalin is usually stated to stop with the production of maltose. 1 

The action of ptyalin in the mouth is necessarily very brief. 
In the stomach the feed comes into contact with the gastric 
juice containing free hydrochloric acid. At first, this acid 
combines with the proteins contained in the feed, but as soon 

1 Carlson and Luckhart (Amer. Jour. Physiol., 23 (1908-9), 149) state that both 
ptyalin and amylopsin produce dextrose from starch. 



DIGESTION AND RESORPTION 93 

as more than a trace of free acid accumulates, or to speak more 
exactly, as soon as the concentration of the hydrogen ions ex- 
ceeds a certain small limit, the action of the ferment is not only 
inhibited, but the ptyalin is digested by the pepsin. 

This, however, is far from happening immediately upon the 
entry of the feed into the stomach. The secretion of the gastric 
juice requires a certain length of time. Moreover, the contents 
of the stomach are semi-solid rather than liquid and while the 
muscular contractions of the stomach serve to mix the feed to 
some extent, this effect is less than is often assumed. Frozen 
sections of animals to which variously colored feeds have 
been given show the contents of the stomach to be distinctly 
stratified some time after the ingestion of feed. Furthermore, 
the gastric juice is secreted only in the pyloric portion of 
the stomach (116). Time is required, therefore, for the 
acid to penetrate and acidify the whole mass and conse- 
quently the action of the ptyalin may continue for a con- 
siderable period. 

Extensive investigations, especially by Ellenberger and 
Hofmeister, upon gastric digestion in the horse and hog have 
demonstrated that in these animals the action of the saliva in 
the stomach upon the starch of the feed plays an important 
part in digestion. In the horse (116), the left end of the stomach 
is really a dilation of the esophagus. In the hog, while nearly 
the entire surface of the stomach is lined with mucous membrane, 
the left-hand end contains no peptic glands. When the stomach 
is filled with feed, therefore, it is evident that the action of the 
hydrochloric acid will begin along the walls of the fundus of 
the stomach and only gradually spread to the rest of the con- 
tents. It is true that lactic fermentation usually sets in during 
this period, aiding to acidify the stomach contents but, as 
already stated, ptyalin is less sensitive to organic than to 
inorganic acids. It has been found that the solution of starch 
may continue to a greater or less extent for as much as four or 
five hours both in the horse and hog. In ruminants, the con- 
ditions are even more favorable for salivary action, since the 
feed remains in contact with the saliva in the rumen for a con- 
siderable time, the contents of this stomach being maintained 
slightly alkaline by the large amount of saliva secreted by these 
animals (115). It may be assumed, therefore, in spite of the 



94 NUTRITION OF FARM ANIMALS 

fact that the saliva of ruminants contains but little ptyalin, that 
a considerable digestion of starch is effected. 

In the duodenum, any starch not digested in the stomach, 
as well as any dextrins, etc., produced by the action of the 
ptyalin, are subjected to the action of the amylopsin of the 
pancreatic juice. This enzym, if not identical with ptyalin, is 
very similar to it but appears to act* more energetically. As 
in the case of ptyalin, the final product of its action is maltose. 1 

The further fate of the maltose resulting from the digestion 
of starch is more conveniently considered along with that of 
other disaccharids in a succeeding paragraph. 

132. Fermentation of starch. — The organisms producing 
the methane fermentation in the digestive tract were believed 
by Tappeiner to attack cellulose specifically and not to act 
upon other carbohydrates. As regards ruminants, however, 
this has been shown to be an error. In G. Kiihn's 2 extensive 
respiration experiments with cattle upon the formation of fats 
from carbohydrates, considerable amounts of starch were added 
to basal rations. Invariably this resulted in an increased ex- 
cretion of methane. Moreover, there was no increase, but on 
the other hand, more or less decrease in the amount of crude 
fiber digested, showing that the additional methane must have 
had its source in the starch consumed. This conclusion is 
confirmed by the fact that the total. excretion of methane was 
quite closely proportional to the sum of the digested crude 
fiber and nitrogen-free extract. On the average four parts of 
methane were produced for each one hundred parts of starch 
digested. Kellner's subsequent investigations 3 have fully 
confirmed these results, although giving a lower average, viz., 
3.07 parts of methane per one hundred parts of digestible 
starch. Moreover, Kellner's investigations have shown that 
the methane fermentation is not confined to cellulose and 
starch but that, as already indicated, the complex of compounds 
grouped under the head of nitrogen-free extract, including the 
sugars, is subject to this process. His experiments also show 
that the proportion of methane produced is somewhat variable, 
depending upon conditions not yet fully investigated. 

As already stated (128), the chief seat of fermentation in the 

1 See footnote on p. 92. 2 Kellner; Landw. Vers. Stat., 44 (1894), 257. 

3 Landw. Vers. Stat., 53 (1900), 423. 



DIGESTION AND RESORPTION 95 

horse is the coecum and colon. Before the feed reaches these, 
however, it has been acted upon by the amylases of the saliva 
and the pancreatic juice and its starch and soluble carbohy- 
drates pretty thoroughly extracted. Consequently, the meth- 
ane production of the horse is substantially at the expense 
of the crude fiber of his feed, although if starch for any reason 
escapes digestion and reaches the ccecum it is doubtless also 
attacked by the bacteria. 

133. The disaccharids. — At first thought, it would seem 
that the carbohydrates of this group need no digestive change, 
since they are already soluble and diffusible and seemingly ready 
to pass into the circulation. But while this is true, they are 
not assimilable by the organism. Disaccharids are nowhere 
found in the normal body fluids and if injected into the circu- 
lation in any considerable amount are voided in the urine. In 
other words, the disaccharids are treated in the organism as 
foreign substances which the cells cannot use. 

In the small intestine the disaccharids are inverted, that is, 
hydrolyzed to monosaccharids. Cane sugar taken in the food 
appears to be inverted to some extent by the acid of the gastric 
juice, but the principal action is by the inverting enzym sucrase 
of the intestinal juice, which splits up the cane sugar into dex- 
trose and levulose. Similarly, the maltose resulting from the 
digestion of starch is split up by the maltase of the intestinal 
juice, yielding dextrose, while lactose, at least in suckling animals, 
is split up by lactase into dextrose and galactose. These in- 
versions appear to take place to a considerable extent in the 
epithelial cells lining the intestines, and this seems to be the 
normal method of assimilation of lactose in many mature ani- 
mals. The epithelial cells are also stated to convert levulose 
and galactose into dextrose. 

Finally it should be added that the sugars, like other carbo- 
hydrates, may undergo the methane fermentation in the first 
stomach of ruminants. 



The digestion of fats 

134. Emulsification. — As already indicated, the digestion 
of fats includes two processes, namely, emulsification and 
saponification, effected chiefly by the action of the bile and 



96 NUTRITION OF FARM ANIMALS 

pancreatic juice. The two processes go hand in hand. As 
explained in Chapter I, the presence of free fatty acids favors 
the formation of a permanent emulsion. As there noted, most 
native fats contain small amounts of such acids which exist 
dissolved in the natural fat. Furthermore, there seems to be 
good evidence that some cleavage of fat into fatty acids and 
glycerol takes place in the stomach of carnivora, while the di- 
gestion of protein in the stomach helps to liberate any enclosed 
fat. When the acid fats come in contact with the alkaline 
pancreatic juice, the molecules of the free acid in solution are 
saponified and in this way the mass of fat is broken up into an 
emulsion. The action of the steapsin of the pancreatic juice, 
which splits fat into glycerol and fatty acids, would obviously 
tend to aid in the emulsification, while, on the other hand, the 
latter, by vastly increasing the amount of surface exposed by the 
fats, tends to aid the action of the enzyms. 

135. Saponification. — The saponification of fat is accom- 
plished essentially by the lipase steapsin of the pancreatic juice. 
As just noted, the saponification is facilitated by the previous 
emulsification, while the presence of the bile is also an important 
factor. It is claimed that the presence of bile is necessary to 
activate the steapsin, while it has also been shown that the 
cleavage of the fats is much accelerated by the presence of bile, 
the effect being ascribed to the lecithins which it contains. The 
presence of bile also assists in the process of digestion by its 
power of dissolving large quantities of fatty acids and of 
their calcium and magnesium soaps. It appears also that the 
bile aids in some way in the resorption of the fat, but just how 
is not clear. 

Fats do not seem to be fermented to any extent in the diges- 
tive tract and when administered to cattle in the form of emul- 
sions have been found to produce no effect upon the excretion 
of methane. When given in substance, they have in some in- 
stances had the effect of diminishing the excretion of that gas. 

The digestion of the proteins and non-proteins 

136. Peptic digestion. — In digestion the proteins are first 
subjected in the stomach to the action of the pepsin and hy- 
drochloric acid of the gastric juice. 



DIGESTION AND RESORPTION 97 

The products of peptic digestion are usually substances be- 
longing to the group of derived proteins (58, 59). The first 
product or products are substances called metaproteins, or, 
according to the older terminology, syntonin or acid proteins. 
By still further action there is formed a succession of proteoses, 
and from these, by subsequent cleavage, peptones. Undoubt- 
edly the products resulting from peptic digestion contain a 
large number of chemical individuals but for the present pur- 
pose it is sufficient to say that the action of pepsin and hydro- 
chloric acid gives rise to the formation of a series of progres- 
sively simpler, more soluble and more diffusible substances. In 
natural digestion, the action extends in the main only as far 
as the production of peptones, although polypeptids seem to 
be also formed to some extent. Amino acids are not found 
among the products of natural peptic digestion, although they 
may be produced by the long continued action of pepsin-hy- 
drochloric acid in artificial digestion. 

The conjugated proteins are split into their two constituents 
and the protein portion is then acted upon like other proteins. 
The gastric juice has no action upon the nucleic acids of the 
nucleoproteins. 

137. Tryptic digestion. — In the duodenum, the proteins 
and the products of their peptic digestion are subjected to the 
action of the trypsin of the pancreatic juice. This is produced 
in the pancreas in the form of a pro-ferment or zymogen, called 
trypsinogen. The presence of pancreatic juice in the duodenum 
stimulates the glands of the latter to the production of the in- 
testinal juice which Pawlow has found to contain a substance, 
enterokinase, which activates the trypsinogen, or converts it into 
trypsin, in some unknown manner. 

The action of trypsin, like that of pepsin, has been largely 
studied in laboratory experiments either with extracts of the 
pancreas or with its secretion as obtained from fistulae. Tryp- 
sin, especially in a neutral or alkaline solution, acts upon pro- 
teins substantially in the same manner as pepsin, causing a 
hydrolytic cleavage and producing at first proteoses and pep- 
tones. It acts much more energetically than pepsin, however, 
and carries the cleavage much further. The action of pepsin 
substantially stops with the production of peptones. Trypsin, 
on the other hand, produces a relatively large amount of the 

H 



98 NUTRITION OF FARM ANIMALS 

simple amino acids out of which the protein molecule is built 
up. Even the most prolonged action of trypsin, however, 
leaves a considerable residue in which no free amino acids are 
found but which on hydrolysis with strong mineral acids yields 
them in abundance. 

Conjugated proteins seem to be acted upon by trypsin in the 
same manner as by pepsin but much more energetically. 

138. Erepsin. — The presence of a proteolytic enzym in 
the intestinal juice and in the epithelial cells of the small intes- 
tine has already been noted (135) . This enzym does not act on 
unaltered proteins, with the exception of casein, but it hy- 
drolyzes proteoses and peptones energetically, yielding crystal- 
line cleavage products. It is of special interest to note that, 
according to Cohnheim, 1 erepsin is capable of effecting the 
cleavage of that part of the protein molecule which is not at- 
tacked by pepsin and trypsin and that in artificial digestion 
experiments almost complete conversion into comparatively 
simple crystalline products may be obtained in a relatively short 
time. 

139. Extent of protein cleavage in natural digestion. — 
When it was first shown by Ktihne and Chittenden that the 
action of trypsin upon proteins yielded among other products 
such simple crystalline substances as leucin and tyrosin, com- 
paratively little importance was attached to the fact from the 
physiological standpoint. While the fact was interesting as 
throwing light upon the chemical structure of the proteins, it 
was believed that in natural digestion the soluble proteoses and 
peptones were promptly removed from the digestive tract by 
resorption and that at most but a small proportion of the feed 
protein underwent any profound cleavage. This belief was 
the stronger because it was believed that only proteins or their 
slightly altered derivatives, the proteoses and peptones, could 
supply the demands of the organism for proteins. Whatever 
protein was broken down into crystalline products was looked 
upon as wasted. With the progress of investigation, however, 
it has become increasingly clear that the processes of hy- 
drolytic cleavage go further and play a much more important 
part than was formerly supposed. While it is admitted that 
peptones, or even soluble proteins, may be resorbed, the weight 

3 Ztschr. Physiol. Chem. 49 (1906), 64; 51 (1907), 415. 



DIGESTION AND RESORPTION 99 

of opinion is that, as a matter of fact, proteins are largely re- 
sorbed in the form of comparatively simple cleavage products ; 
not necessarily in every case as simple amino acids but at least 
in the form of comparatively simple peptids. 

The nucleic acids derived from the peptic or tryptic diges- 
tion of the nucleoproteins are split by the nucleases of the in- 
testinal juice into mononucleotids and these again by the 
nucleotidases of the same secretion into nucleosids (53). No 
digestive enzyms attacking the latter class of compounds are 
known, but they are split to some extent by intestinal bacteria 
into pentoses and purin or pyrimidin bases. Furthermore, it has 
been found that extracts of the intestinal mucous membrane 
(epithelial cells) possess the power of bringing about the same 
cleavages which are accomplished by the enzyms of the in- 
testinal juice, and in addition are able to split the resulting 
nucleosids into pentose and base. It appears, then, that the 
final digestive products of the nucleic acids are, as in the case 
of the simple proteins, relatively simple substances, viz., phos- 
phoric acid, pentoses, and purin and pyrimidin bases. 

140. Putrefaction of proteins. — Attention has already been 
called, in connection with the digestion of the carbohydrates, 
to the bacterial flora of the digestive tract. The carbohy- 
drates, as was shown, are acted upon chiefly by the organisms 
producing the methane fermentation. Proteins and their de- 
rivatives, on the other hand, have been shown by Kellner to 
contribute practically nothing to this fermentation in the case 
of cattle. They are, however, especially subject to the action 
of the organisms producing putrefaction. The action of such 
organisms is prevented in the stomach by the hydrochloric acid 
of the gastric juice. In the small intestine they become more 
active, especially as the feed reaches the lower portion, while 
their activity lessens again as the lower portion of the large in- 
testine is reached, owing to the progressive resorption of water 
from the intestinal contents. The characteristic products of 
the putrefaction are ammonia and certain aromatic compounds 
derived from the heterocyclic components of the proteins (47). 

The aromatic products of putrefaction (indols and phenols) 
are found in part in the feces but are in large part resorbed. 
They cannot, however, be utilized by the organism but, on the 
contrary, are poisonous and are therefore combined with other 



IOO NUTRITION OF FARM ANIMALS 

substances which render them innocuous. In particular, they 
unite with sulphates to form the so-called ether-sulphates which 
are excreted in the urine. The amount of these substances in 
the urine furnishes a convenient index to the extent of intestinal 
putrefaction. 

141. The non-proteins. — As ordinarily determined (61, 
106), the non-proteins constitute a group of nitrogenous sub- 
stances soluble in water, many of which are identical with or 
closely related to the final products of the digestion of the 
proteins. Accordingly, they have generally been assumed to 
be ready for resorption without further action by the digestive 
juices and therefore to be entirely digestible. 

It has been shown, however, that, in ruminants at least, the 
matter is by no means so simple as the mere resorption of water- 
soluble substances. In the capacious first stomach of these 
animals, the non-proteins play an important role as a supply 
of nitrogenous food for the organisms which are so abundant 
there. This has several consequences. 

In the first place, it appears that these soluble compounds 
are more readily attacked and utilized by the organisms than 
are the true proteins of the feed. The presence of non-proteins, 
therefore, tends to protect the proteins from bacterial decom- 
position. 

In the second place, an abundant supply of soluble nitrogenous 
matter stimulates the multiplication and activity of the or- 
ganisms and so brings about a more extensive fermentation of 
the carbohydrates of the feed, as is evidenced by an increase 
in the methane given off and in the proportion of the carbo- 
hydrates apparently digested. 

Third, it seems to be fairly well made out that the nitrogen 
which these organisms assimilate is utilized to build up their 
protoplasm and thus, by a sort of symbiosis, becomes a source 
of protein to their host. It has been claimed that this bacterial 
protein is indigestible, but the evidence on which this claim 
is based is capable of a different interpretation and there seems 
to be good reason for believing that it may be acted on in the 
stomach and intestines by the digestive enzyms like other pro- 
teins and serve as a source of protein to the body. Some of 
the evidence in favor of this view is presented in a subsequent 
discussion of the nutritive value of the non-proteins (786-789). 



DIGESTION AND RESORPTION IOI 

The digestion of ash 

The various digestive enzyms whose action has been con- 
sidered in the foregoing pages bring about extensive chemical 
changes in the organic nutrients of feeding stuffs by means of 
which they are prepared to enter into the nutritive processes 
in the tissues. At the same time, the so-called " inorganic " 
ingredients of feed are also prepared for resorption, but the di- 
gestion of these substances has been less extensively studied 
than that of the organic nutrients. 

142. Sulphur and phosphorus. — As regards the sulphur of 
the proteins, it does not appear that this element is separated 
from its union with carbon, nitrogen and hydrogen in the pro- 
cesses of protein digestion. The sulphur of the proteins is con- 
tained in the amino-acid cystin, which, so far as known, is 
resorbed without further change. As regards the phosphorus of 
the nucleo-proteins, opinions still differ as to whether it is split 
off as phosphoric acid in the course of digestion or resorbed, still 
in " organic " combination, as a nucleosid. To what extent 
other ash ingredients are taken up, like sulphur and phosphorus, 
in organic combination, it is difficult to say, but that such re- 
sorption takes place is to be regarded as probable. 

143. Electrolytes. — As regards those ash ingredients of 
feeds which are present as electrolytes, it may be assumed that 
they are brought into solution to a greater or less extent by the 
hydrochloric acid of the gastric juice, but how much reprecipi- 
tation may occur in the more or less alkaline contents of the 
intestine it is difficult to say. The whole subject of the diges- 
tion of the ash ingredients of feeding stuffs, however, is so in- 
timately related to the question of the paths of excretion and to 
the problems of ash metabolism that it can be more profitably 
considered in that connection. 

Summary of changes in digestion 

144. Solution of nutrients. — The substances which make 
up the larger part of the feed of domestic animals (and of man 
as well) are comparatively insoluble in water. Some of them, 
such as cellulose and the fats, may be regarded as practically 
entirely insoluble. Others, like starch and the proteins, are 



102 NUTRITION OF FARM ANIMALS 

very sparingly so. While small amounts of soluble proteins 
and somewhat larger quantities of soluble carbohydrates occur, 
they ordinarily play but a subordinate role in nutrition. One 
obvious result of the chemical changes brought about by the 
enzyms and organized ferments of the digestive tract is to 
convert these insoluble substances into soluble ones. Thus 
starch yields sugar, cellulose the organic acids, fats form 
soaps and protein yields peptones and amino acids. It was 
natural, therefore, that digestion should be looked upon as 
a process of solution and compared to the preparation of 
extracts in a pharmaceutical laboratory by means of various 
solvents. 

The solvent action of the digestive juices is important, since 
the animal, like the plant, absorbs its real food substances 
substantially in aqueous solution. The mere dissolving of the 
ingredients of the feeds, however, is far from being the only or 
even the chief function of the digestive juices, as is clearly 
indicated, for example, by the existence of a coagulating enzym 
like chymosin, which precipitates the soluble casein, or the pres- 
ence of the various invertases, which attack substances already 
soluble. 

145. Colloids converted into crystalloids. — The principal 
nutrients belong to the class of substances called colloids. 
Gelatin is a typical colloid as are, indeed, all the proteins and 
the more abundant carbohydrates, while the sugars, organic 
acids, etc., are classed as crystalloids. 

As related to digestion, the most important distinction be- 
tween colloids and crystalloids is the difference in the osmotic 
pressures of their solutions by virtue of which crystalloids 
diffuse readily through permeable membranes. This diffusi- 
bility plays an important part in the resorption of the digested 
material into the blood and lymph current, as will appear in the 
next section, although it is by no means the only factor con- 
cerned. 

A review of the chemical changes which take place in diges- 
tion shows that they are all in the direction of molecular simplifi- 
cation. They are substantially processes of cleavage by which 
large molecules are split into two or more smaller ones. Such 
a change, however, is in the direction from the colloid to the 
crystalloid condition. The final products of digestion are 



DIGESTION AND RESORPTION 103 

mostly substances of comparatively low molecular weight, 
readily soluble in water and having a relatively high osmotic 
pressure and therefore readily diffusible. This difference is 
most marked in some of the more simple cleavage products of 
the proteins and least so in the case of the digestive products 
of the fats. 

146. Uniformity in nutritive material. — The feed consumed, 
especially by herbivora, is of a very heterogeneous character. 
The proteins and carbohydrates in particular are present in 
great variety, so that the nature and proportions of the sub- 
stances out of which the body must draw the material for the 
construction and maintenance of its tissues may vary greatly 
at different times. Under the action of the digestive enzyms, 
however, these diverse substances all yield substantially the 
same products so that the nutritive solution supplied to the body 
proper is qualitatively of a very uniform composition, contain- 
ing chiefly monosaccharids, various acids of the aliphatic series, 
amino acids derived from the proteins, and the soluble ash in- 
gredients. By this preliminary action upon the feed in the 
digestive canal, — i.e., practically outside the body, — the 
organism is rendered independent of the particular kinds of feed 
available, its cells being constantly supplied with uniform 
nutritive material. 

147. Molecular simplification. — It has just been pointed 
out (145) that digestion from the chemical standpoint consists 
substantially of a series of hydrolytic cleavages of the nutrients, 
yielding compounds of lower molecular weight and greater solu- 
bility and diffusibility. This molecular simplification has, 
however, a more important aspect which is most strikingly 
illustrated in the case of the proteins. It was shown in Chap- 
ter I that the proteins, although very similar in many physical 
properties, may differ widely from each other as regards molecu- 
lar structure. This is shown in the first place by the wide 
variations in the proportions of the constituent amino acids 
which they yield on hydrolysis (50). Moreover, even were 
these cleavage products present in the same proportions, the 
existence of optical isomers and the possible variations in the 
order and manner of linkage of the amino acids afford almost 
endless possibilities of isomerism. Studies in immunity have 
in fact revealed striking specific differences between proteins 



104 NUTRITION OF FARM ANIMALS 

bearing the same name but derived from different species or 
different individuals of the same species, the proteins of one 
animal often being toxic to another. 

The body proteins, then, are specific both as to composition 
and structure and differ in both respects from those of the feed. 
In order that the latter may nourish the organism they must be 
converted into the specific proteins of the body. This is accom- 
plished through their cleavage in the digestive tract into their 
constituent " building stones " which the body may then 
reassemble to form proteins constructed according to its own 
specific pattern. Not only so, but the proteins of different 
tissues or even cells must be regarded as specific. The body 
proteins are built not after a single pattern but after numerous 
ones. It is only by a very extensive, even if not complete 
(139), breaking down of the structure of the feed proteins that 
it becomes possible for the body to build up out of the fragments 
the various proteins which it requires. " Its protein mole- 
cules have a different architecture from those of the plant." 
This fact throws an interesting light upon the coagulation of 
the soluble casein of milk in the stomach. Although present 
in soluble form, it is not a body protein and its coagulation 
serves to retain it in the digestive tract and give the proteolytic 
enzyms an opportunity to break it up 'into its constituent 
amino acids. 

What is so strikingly true of the proteins is likewise true of 
other nutrients. The digestive cleavages serve not merely, 
or perhaps not chiefly, to render them soluble and diffusible 
but to reduce the molecular complexes to forms which the body 
cells can assimilate. The carbohydrates, e.g., are converted 
into monosaccharids, even the somewhat larger molecules of 
the disaccharids appearing to be too large or to have an un- 
suitable molecular structure for the body cells to use. In 
general the complex compounds of the feed are split up by the 
enzyms of the digestive fluids into their constituent atomic 
groupings or " building stones " which supply the material out 
of which the body by selection and rearrangement builds up 
the proteins, carbohydrates and fats peculiar to itself, and the 
value of a feed depends upon the nature and amounts of the 
cleavage products which it yields in digestion rather than upon 
the specific substances which it contains. 



DIGESTION AND RESORPTION 



I05 



§ 3. Resorption — The Feces 

148. Definition. — As was stated at the beginning of this 
chapter (113), the digested feed contained in the alimentary 
canal is really outside the body, just as in the case of the ameba. 
In order to enter the body, the digested material must pass 
through or be taken up by the cells surrounding the digestive 
cavity. The process by which the products of the digestion of 
the feed are transferred from the digestive organs to the circulat- 
ing media (blood and lymph) of the body is called resorption. 

149. Epithelium. Villi. — The inner, or mucous, membrane 
of the digestive tract bears on its surface a layer of epi- 



Epithelium 
of villus. 



Artery of 

villus. 




" Central chyle- 
vessel of vil- 
lus. 



Chyle-vessel. 



Fig. 14. — Section of villi. (Bohm, Davidorf, Huber, Text Book of Histology.) 

thelial cells, more or less resembling those lining the mouth, which 
is closely underlaid with a network of blood capillaries and 
lymph vessels. It is these epithelial cells which are the active 
agents in resorption. 



106 NUTRITION OF FARM ANIMALS 

In the higher animals the extent of resorbing surface is greatly 
increased by certain projections of the interior surface of the 
small intestine known as the villi. Those are round or club- 
shaped protuberances of the inner surface of the intestine. 
They are covered, like all parts of the intestinal surface, with the 
epithelial cells just described, which are underlaid by a deli- 
cate membrane, beneath which are found numerous minute 
capillary blood-vessels, a layer of smooth (involuntary) mus- 
cular fibers and a network of nerves. In the center of each 
villus ends a vessel called a lacteal, belonging to the lymphatic 
system. Figure 14 shows a longitudinal section of three villi. 

The villi are absent in the stomach and in the large intestine. 
Although some resorption takes place in the stomach, and while 
a considerable amount of water and more or less of the fermen- 
tation products are resorbed in the large intestine, the small 
intestine is the special resorptive organ. 

150. Mechanism of resorption. — Since the processes of 
digestion are apparently directed toward the conversion of feed 
substances into soluble and diffusible forms, it was quite natural 
that resorption should be regarded as an osmotic process. In 
this conception of it, the epithelial cells and other tissues be- 
tween the cavity of the digestive organs and the blood and lymph 
vessels constituted a membrane through which osmosis took 
place. On the one side of this membrane were the contents 
of the digestive tract, containing the soluble products of diges- 
tion, while on the other side were the blood and lymph, contain- 
ing little or none of these products. Under these conditions, 
osmosis was assumed to set in and transfer the digested nutrients 
to the blood and lymph. 

Undoubtedly osmosis plays an important part in resorption, 
but its effects are profoundly modified by the properties of the 
resorbing cells of the intestinal epithelium in ways which as yet 
are but very partially understood, and resorption can by no 
means be explained by a simple analogy with the parchment 
dialyzing tube of the laboratory. 

Differences in the permeability of the epithelial cells and of the 
intercellular substance for the various dissolved substances in the 
digestive tract doubtless play their part in bringing about the phe- 
nomena of selective resorption, while variations in the affinity of the 
cell colloids for water may be assumed to influence the resorp- 



DIGESTION AND RESORPTION 1 07 

tion of that substance as well as of salts. There are other facts, 
however, for which it is difficult at present to offer any physico- 
chemical explanation. Notable among these is the predominant per- 
meability of the intestinal epithelium in one direction, viz., from the 
intestinal lumen towards the blood and lymph vessels. 

For the present, it is necessary to be content with the state- 
ment that resorption is a function of the living epithelial cells, 
although such a statement, of course, explains nothing but 
simply means that it is impossible at present to form an adequate 
conception of the intimate mechanism of the process. 

Resorption might be characterized briefly as a reverse se- 
cretion. In secretion the active cells of a gland take materials 
from the blood or lymph, transform them into the specific 
substances characteristic of the cells, and then eject the latter 
into the duct of the gland. The epithelial cells of the digestive 
tract, on the other hand, take up digested materials from the 
contents of the alimentary canal, modify them more or less 
chemically and transmit the products to the blood or lymph. 

151. Paths of resorption. — Most of the resorbed substances 
seem to pass from the epithelial cells to the blood in the capil- 
laries and thus finally through the portal vein (182) to the liver. 
This is true of the cleavage products of the proteins, of carbo- 
hydrates, organic acids, salts and water. Fats, on the other 
hand, enter the circulation chiefly or wholly through the lymph 
in the form of minute droplets which are secreted by the epi- 
thelium into the lacteals of the villi, whence they pass through 
the lymphatics to the thoracic duct (186). 

152. Chemical changes in resorption. — It is somewhat 
generally believed that the products of digestion, especially of 
the proteins and fats, undergo rather extensive chemical changes 
in the epithelial cells during the process of resorption. This 
question is considered more particularly in Chapter V but may 
be briefly referred to here for the sake of completeness. 

Proteins. — In digestion the proteins yield comparatively 
simple cleavage products. It has been maintained, especially 
by Abderhalden and his school, that these cleavage products 
are resynthesized in the epithelial cells into serum albumin, 
which is regarded as the common source of all the body proteins. 
This view has been based chiefly on the failure to detect amino 
acids or other protein cleavage products in the blood coming 



108 NUTRITION OF FARM ANIMALS 

from the intestines even during the height of protein resorption. 
Folin and Denis and also Van Slyke and Meyer have recently 
demonstrated, however, that sufficiently delicate tests show 
the presence of such products in the portal blood in amounts 
as large as could be expected in view of the gradual nature of 
digestion and resorption and of the large volume of blood pass- 
ing through the intestinal capillaries. The prevailing opinion 
seems to be at present that the digestive products of the pro- 
teins undergo relatively little modification before entering into 
the circulation. 

Fats. — The mechanism of fat resorption has been the subject 
of heated controversy. Some physiologists have maintained 
that it is chiefly a physical process ; that globules of emulsified 
feed fat are taken up bodily by the epithelial cells and excreted 
again by them into the lacteals. This view is based largely 
on microscopical observations which show the presence of ap- 
parently unaltered fat globules of the intestinal emulsion in 
the protoplasm of the epithelial cells and in the lymph of the 
lacteals after the ingestion of fat. Other no less eminent physi- 
ologists, however, have as stoutly held that fats are not resorbed 
unaltered but only after cleavage into glycerol and fatty acids 
(or their salts), which are soluble in bile (135), and that the fat 
globules observed in the epithelial cells are the product of a 
resynthesis. At present the weight of scientific opinion is 
strongly in favor of this latter view. It is perhaps true that 
unaltered fat droplets may be taken up by the epithelial cells 
but that any considerable amount of fat is resorbed in this 
fashion is to say the least very questionable. 

At any rate, the digested fat reaches the lacteals almost en- 
tirely in the form of fat, so that after a meal containing much 
fat the lacteals are filled with a milky fluid and the lymph is 
found to contain relatively large amounts of neutral fats. It 
is clear, then, that the resorbed soaps and fatty acids are speedily 
synthesized to fat again. This synthetic power is still further 
and strikingly demonstrated by the fact that free fatty acids 
are readily digested but are transmitted to the lacteals in the 
form of the corresponding neutral fats, having evidently been 
combined with glycerol in the process of resorption, although 
the source from which the body derives its glycerol is still un- 
certain. Evidently, then, from this point of view, nothing 



DIGESTION AND RESORPTION 1 09 

stands in the way of the supposition that the digested fats are 
completely split up into glycerol and fatty acids in the process 
of digestion and synthesized again in the epithelial cells, although, 
on the other hand, of course, it does not prove that such is the 
case. 

153. The feces. — As the contents of the digestive tract move 
forward through the small and large intestines they become 
progressively more and more impoverished in digestible material 
and also, in the lower portion of the large intestine, are deprived 
of part of their water, so that there accumulates in the rectum 
a more or less solid residue which is voided at intervals as the 
feces. 

The feces are to be regarded as both an excretory product 
(198) and a feed residue. 

154. The feces as an excretory product. — The fact that the 
feces are an excretory product is most obvious in the carnivora, 
whose normal feed consists of substances almost wholly diges- 
tible, but it is evident also in man. On a pure meat diet, for 
example, feces continue to be produced in which undigested 
feed residues are either absent entirely or present in minimal 
amounts only. Even a fasting animal continues to produce 
feces, while an empty loop of the intestine, separated from the 
remainder of the digestive tract, soon fills up with fecal-like 
material. 

The excretory ingredients of the feces include unresorbed 
digestive juices and their decomposition products, intestinal 
mucus, worn-out epithelial cells and cell fragments, leucocytes 
and excretions of the intestinal mucosa. Especially notable 
among the latter are salts of calcium and of iron and in herbivora 
the phosphates of calcium and magnesium. The feces also 
include a not inconsiderable proportion of intestinal micro- 
organisms. 

155. The feces as a feed residue. — The ordinary mixed 
diet of man, and to a much more marked degree the ordinary 
feed of herbivorous animals, contains relatively considerable 
amounts of materials which are either indigestible or which for 
one reason or another escape digestion and therefore reappear 
in the feces. Among these, some, like lignin, cutin, the waxes, 
chlorophyl and other non-fatty ingredients of the " ether 
extract," and the insoluble ash ingredients, may be regarded 



HO NUTRITION OF FARM ANIMALS 

as wholly indigestible. Of more importance, however, are 
such carbohydrates as cellulose and the various hemicelluloses, 
the levulans, galactans, mannans, pentosans, etc., which 
may be said to be practically only partially digestible. 
By this is not meant, of course, that one molecule of cellulose, 
e.g., is any less digestible per se than another, but only that 
part of the cellulose of ordinary feeds does as a matter of fact 
escape digestion, largely because the length of time during 
which it is exposed to the action of the organisms which attack 
it is insufficient to allow of its complete solution. The feces of 
herbivorous animals, therefore, contain amounts of these di- 
verse carbohydrates varying with the character of the feed and 
the activity of the fermentation processes in the digestive tract. 
Since these compounds are especially abundant in the roughages, 
the feces from these feeds are bulky and especially rich in un- 
digested " crude fiber." 

Other ingredients, particularly of vegetable feeding stuffs, 
partially escape digestion not on account of any lack of the ap- 
propriate digestive enzyms but because they are mechanically 
protected from the action of the latter. If granules of starch, 
e.g., are contained within a cell which has not been ruptured 
during the mastication of the feed, the cell wall tends to protect 
them from the action of the digestive juices, and they may escape 
digestion although per se entirely digestible. The extent to 
which such a nutrient will actually be digested, therefore, will 
depend to a considerable degree upon whether the cellulose of 
the cell wall is attacked and destroyed by the organisms of the 
alimentary canal. What is true of starch in this respect is 
obviously true of all cell enclosures, and explains why more or 
less matter intrinsically digestible may be rejected in the feces. 
For a like reason, seeds which escape mastication are but im- 
perfectly digested, being protected by the relatively insoluble 
seed coats. Similarly, cellulose itself may be so impregnated 
with lignin and cutin substances that the " crude fiber " may 
be attacked only with difficulty or not at all by the methane 
fermentation. 

Finally, there is to be considered the possibility of a mis- 
proportion between digestion and resorption. In heavy rations, 
especially, substances which are actually digested may per- 
haps escape resorption through insufficient contact with the 



DIGESTION AND RESORPTION III 

intestinal walls or from lack of time, and so be found in the 
feces. 

156. Composition of feces. — Evidently the feces are a very 
complex and variable mixture, including, on the one hand, the 
various excretory products just enumerated and, on the other 
hand, indigestible feed substances and digestible materials 
which have for one reason or another escaped actual digestion 
or which, having been digested, have failed of resorption. 
Among the latter may be included unresorbed products of the 
putrefaction of the proteins, especially skatol, which impart 
to the feces their offensive odor. 

The proportions of these two groups — the excretory products 
and the feed residues — in the feces vary widely with the 
nature of the feed consumed. In the carnivora the body wastes 
predominate, so that the feces of these animals are to be regarded 
as primarily an excretory product. To a considerable degree 
the same thing is true of man, especially when living on a con- 
centrated diet. With the herbivora, on the contrary, the in- 
digestible or undigested feed residues constitute the bulk of 
the feces, although the amount of true excretory products is 
by no means insignificant. Omnivora like the hog occupy an 
intermediate position in this respect. 

§ 4. The Determination of Digestibility 

157. Definition of digestibility. — The words digestible and 
digestibility are used in more than one sense. Sometimes, for 
example, a food is said to be digestible because it is easily di- 
gested — that is, causes no unpleasant sensation after it is 
eaten — while by an indigestible food is meant one that is apt 
to cause gastric or intestinal disturbances. Again, it is not un- 
common to judge of the digestibility of stock feeds by their 
effects and to regard that one as the more digestible which causes 
or seems to cause the greater gain in weight. 

The word digestibility as used in the study of animal nutrition, 
however, has a definite and limited meaning. It denotes the 
percentage of the feed, or of any single ingredient of the feed, 
which is dissolved or otherwise acted on in the digestive canal 
so that it can be resorbed and thus put at the disposal of the 
body cells. For example, the digestion experiment with a steer 



112 NUTRITION OF FARM ANIMALS 

described in a subsequent paragraph (160) showed that out of 
each ioo grams of protein in the clover hay eaten by the animal 
53 grams were apparently digested and resorbed. The digesti- 
bility of the protein in this case, therefore, is said to be 53 per 
cent. Digestibility in this sense is obviously a conception 
entirely distinct from that of rapidity or ease of digestion. A 
feed may have no injurious nor disagreeable effects and yet 
may have a low percentage digestibility — straw, for example. 

Neither does the percentage digestibility alone determine 
the effect produced by a feed. Two feeds may be equally di- 
gestible and yet one may be more valuable than the other be- 
cause its digested matter can be used to better advantage by 
the body. Nevertheless, it is clear that the indigestible 
portion of the feed can make no- contribution to the nutrition 
of the body. The first step, therefore, although by no means 
the last one, in comparing the values of different feeds or rations 
is to determine as accurately as possible what proportion of 
each ingredient is capable of digestion. In other words, we 
shall seek to add to the qualitative knowledge of the processes 
of digestion and resorption outlined in the preceding sections 
a quantitative knowledge of the extent of digestion. 

158. Method of digestion experiments. — The percentage 
digestibility of feeding stuffs can, as a rule, be determined only 
by trial with an animal. Such trials are called digestion ex- 
periments, and a brief outline of the way in which they are made 
will aid in understanding just what is meant by digestibility. 

The method is substantially that originated by Henneberg 
and Stohmann in their early investigations (707). Since it is 
obviously impossible to collect and measure the substances 
digested and resorbed from the feed, it is necessary to have 
recourse to an indirect method, viz., to determine what portions 
of the feed are not digested and compute by difference the 
amounts digested. As already stated (155), the undigested 
portions of the feed are excreted in the feces. A digestion 
experiment really consists in determining as exactly as may be 
how much of the feed is thus rejected, any portions of it which 
disappear during its passage through the alimentary canal being 
regarded as digested. 

If the feces consisted only of undigested feed residues, the 
matter would be very simple, but they also include a greater or 



DIGESTION AND RESORPTION 



113 



less proportion of excretory products (154). In the case of 
herbivora, the proportion of the latter is relatively small and 
in the digestion experiment as ordinarily conducted is neglected, 
it being assumed, in other words, that the feces are equivalent 
to undigested feed residues. The same method is pursued in 
digestion experiments with swine, although in these animals 
the proportion of excretory products in the feces is larger. The 
error thus introduced into digestion experiments is not negligible, 
especially as regards certain ingredients. It will be convenient, 
however, to take up first the methods of digestion experiments 
as ordinarily conducted and to consider later the nature and 
extent of the errors introduced by neglecting the presence of the 
excretory products. 

159. Time required for digestion experiments. — It is es- 
sential that a digestion experiment be preceded by a prelimi- 




Fig. 15. — Steer in digestion stall. (Bailey's Cyclopedia of American Agriculture.) 



nary period in which the feed to be investigated is fed in the same 
weighed amounts daily as in the actual experiment. This is 
for the purpose of removing from the digestive tract residues 



114 NUTRITION OF FARM ANIMALS 

of previous feeds and also of establishing as uniform a rate of 
excretion of feces as practicable. In the case of ruminants, such 
a preliminary period should extend over one or two weeks, while 
with swine it may be made somewhat less. In the succeeding 
digestion experiment proper, the same feeding is continued 
and the feces are collected quantitatively for a number of days 
(seven to ten or more), in order to eliminate the error due to the 
irregularity of the excretion from day to day. From the 
weights of feeds and feces and their composition as determined 
by analysis, the digestibility is computed as illustrated in the 
following paragraphs. 

160. Example of a digestion experiment. — A steer was fed 3.7 
kilograms of clover hay per day for three weeks. During the last 
ten days of this time, the average weight of the daily feces was 5.662 
kilograms. Samples of each were analyzed and found to contain 
the following percentages of dry matter. 

Clover hay 84.97 P er cen t 

Feces 22.36 per cent 

The 3.7 kilograms of hay, therefore, contained 3.144 kilograms of 
dry matter while the 5.662 kilograms of feces excreted contained 
only 1.267 kilograms of dry matter. The difference, 1.877 kilograms, 
which did not appear in the feces, is regarded as having been digested 
by the steer. This amount is 59.7 per cent of the 3.144 kilograms 
eaten ; we say, then, that the percentage digestibility of the dry 
matter of this hay was 59.7 and this number is sometimes called its 
' ' digestion coefficient . ' ' 

In precisely the same way the percentage digestibility of each in- 
gredient may be computed from the results of analyses of the hay 
and of the feces, which in this case gave the following results : — 

Hay Feces 

Water 

Ash 

Protein 

Non-protein 

Crude fiber 

Nitrogen-free extract 

Ether extract 



1 All the nitrogen of the feces is here assumed to exist in the form of protein, an 
assumption which, as will appear later, is far from being true (166), but which 
does not affect the method of computation. 



% 


% 


1503 


77.64 


5-49 


1.92 


10.24 


3-13 l 


1.36 


— 


28.61 


9.29 


36.98 


7-5o 


2.29 


0.52 


100.00 


100.00 



DIGESTION AND RESORPTION 



115 



These figures, together with the weights of hay eaten and feces 
excreted per day, yield the following results : — 

Table 20. — Results of a Digestion Experiment 





Dry 
Matter 

Kgs. 


Ash 
Kgs. 


Pro- 
tein 

Kgs. 


Non- 
Protein 

Kgs. 


Crude 
Fiber 

Kgs. 


Nitro- 
gen 
Free 
{ Ex- 
tract 

Kgs. 


Ether 
Ex- 
tract 

Kgs. 


In hay eaten . . . 
In feces excreted . . 


3-144 
1.267 


0.203 
0.109 


o.379 
O.I77 


0.050 


1.059 
0.526 


1.368 
0.425 


0.085 
0.030 


Difference = digested 
Percentage digesti- 
bility 


1.877 
59-7Q 


0.094 
46.48 


0.202 
S3-!9 


0.050 
100.00 


0-533 

50.27 


0-943 
68.94 


0.055 
65.02 



161. Digestibility of concentrates. — The method just outlined 
for determining the digestibility of a roughage or of a total ration 
is in conception very simple. The determination of the digestibility 
of concentrates by herbivora is somewhat more complicated, since 
they cannot be made the sole feed of these animals. They must, 
therefore, be fed along with a known amount of a roughage whose 
digestibility by the same animal is likewise determined in a preced- 
ing or following period. From the digestibility of the total ration 
and the known digestibility of the roughage that of the concentrate 
is obtained by means of a second calculation by difference. 

Thus, the same steer used in the experiment of the preceding para- 
graph received per day in a subsequent period the same amount, 3.7 
kilograms, of clover hay and in addition 4 kilograms of maize meal. 
The average daily excretion of feces on this mixed ration was 8.715 
kilograms. An analysis of the clover hay used in this period showed 
but slight variations from that of the preceding period. The com- 
position of the maize meal and of the feces was : — 



Water 

Ash 

Protein .... 
Non-protein . . . 
Crude fiber . . . 
Nitrogen-free extract 
Ether extract . . 



aize Meal 


Feces 


% 


% 


13-73 


81.91 


1.25 


1.77 


8.80 


3.66 


0.25 


— 


1.89 


6.51 


70.44 


5.71 


3-64 


0.44 


100.00 


100.00 



Il6 NUTRITION OF FARM ANIMALS 

The digestible matter contained in the total ration, computed 
exactly as in the previous example, was as shown in the first part 
of Table 21. If, now, it be assumed that the digestibility of the 
clover hay was unaltered by the addition of the maize meal, it is 
possible to compute how much of each kind of digestible matter (pro- 
tein, crude fiber, nitrogen-free extract, etc.) in the total ration was 
derived from the hay ; the remainder, therefore, must have come 
from the maize meal and by comparison with the total amounts 
present in the latter the percentage digestibility is computed. 

It is evident that the determination of the digestibility of a con- 
centrate in this way is less accurate than that of a feed which can be 
given by itself. The assumption that the digestibility of the roughage 
is not changed is unproved and probably not strictly correct. More- 
over, any errors arising from this source and likewise all the errors in 
weighing and analysis are, by the method of calculation, assigned to 
the concentrate. The writer has shown 1 that the range of uncer- 
tainty thus introduced may be very wide. It will evidently be 
greatest when the proportion of concentrate to roughage is least and 
will affect most those ingredients of the concentrate which are present 
in the smallest proportion, such as crude fiber and often ether extract. 
In extreme cases, absurd results are sometimes obtained, such as 
negative digestibility or a digestibility greater than 100 per cent. 

162. Laboratory determination of digestibility. — Actual 
digestion experiments upon animals according to the method 
just outlined, while simple in principle, require special facilities 
and a considerable expenditure of time. It would obviously 
be very desirable to possess methods by which the action of the 
digestive fluids of the body could be imitated in the laboratory 
and the digestibility of feeds thus determined in a simpler 
and more expeditious manner. 

Numerous attempts have been made to solve this problem, 
but as yet a satisfactory method has been worked out only 
for protein, while attempts to devise similar methods for the 
non-nitrogenous ingredients of feeding stuffs have not yet 
proven successful. The method for protein is based upon 
suggestions made long ago by Stockhardt and by Hofmeister, 
but was first put into practical form by Stutzer. 2 It consists 
in treating the feed with a solution of pepsin and hydrochloric 
acid under specified conditions and determining the undissolved 
nitrogen in the residue. The difference between this and the 

1 Amer. Jour. Sci., 29 (1885), 355. 2 Jour. Landw., 28 (1880), 195 and 435. 



DIGESTION AND RESORPTION 



117' 



Table 21. — Computation of the Digestibility of a Concentrate 



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Il8 NUTRITION OF FARM ANIMALS 

r 

total nitrogen of the feed represents, of course, the amount of 
nitrogenous matter which has been dissolved and which, there- 
fore, is regarded as digestible. 

Comparisons by Kellner, 1 Pfeiffer, 2 G. Kiihn 3 and others between 
the natural and artificial digestion of protein have shown that the 
former method gives lower results on account of the presence in the 
feces of nitrogenous excretory products (154, 158), but that when a 
correction is made for the latter in the manner indicated on a subse- 
quent page (166) the results of the two methods show a substan- 
tial agreement. In other words, the method of artificial digestion 
shows with a good degree of accuracy the true as compared with the 
apparent digestibility (163, 167) of the protein. 

163. Influence of excretory products on apparent digesti- 
bility. — Since the digestion experiment as ordinarily conducted 
ignores the presence in the feces of excretory products, the re- 
sults obtained by its use will necessarily be too low, since sub- 
stances are reckoned as undigested ingredients which really are 
not such. Obviously, the ingredients most affected by this 
error will be those which, on the one hand, are contained in 
the feed in the smallest proportion and which, on the other 
hand, are relatively most abundant among the excretory 
products in the feces. These ingredients are, when the or- 
dinary scheme of feeding stuffs analysis is followed, ash, ether 
extract and nitrogenous substances. As regards the crude 
fiber, on the other hand, this error is absent, since obviously 
no crude fiber is included among the excretory products, and it 
seems probable that substantially the same thing is true of 
the nitrogen-free extract. 

164. Digestibility of ash ingredients. — Certain ash in- 
gredients, particularly iron, calcium, magnesium and phos- 
phorus, are largely or wholly excreted from the body in the 
feces (199). Furthermore, the resorption of the ash ingredients 
of the digestive juices may not be complete and these residues 
may be added to the ash content of the feces. The ordinary 
digestion experiment, therefore, affords little information as to 
the extent to which the ash ingredients of the feed are actually 

1 Centbl. Agr. Chem., 9 (1880), 763. 

2 Jour. Landw., 33 (1885), 149; 34 (1886), 425. 
3 Landw. Vers. Stat., 44 (1894), 188. 



DIGESTION AND RESORPTION 119 

digested and resorbed and this fact constitutes a serious dif- 
ficulty in the study of the ash metabolism. 

165. Digestibility of ether extract. — Among the excretory 
products contained in the feces are included ether-soluble 
substances, especially those derived from unresorbed bile con- 
stituents. While their total amount is small, the feed of farm 
animals is also usually poor in ether extract and consequently 
the error in the computation of the percentage digestibility 
may be relatively large. Indeed, not a few instances are on 
record in which the ether extract of the feces has exceeded 
that of the feed. Little definite knowledge is available, however, 
as to the actual extent of the error thus introduced, but it is of 
relatively less importance in view of the small role which fat 
plays in the ordinary rations of farm animals. 

166. Digestibility of nitrogenous substances. — Most of the 
excretory products in the feces (154) are nitrogenous substances 
and it is particularly with reference to their influence upon the 
determination of the digestibility of the nitrogenous constituents 
of feeding stuffs that investigation has been active. That they 
may seriously affect it is evident from the results obtained in 
numerous experiments upon feeding stuffs poor in protein, such 
as straw, in which a negative digestibility of the crude protein 
has been observed, — i.e., in which the feces have contained 
more nitrogen than the feed. Moreover, experiments upon 
rations containing no nitrogen at all have shown that under 
these conditions nitrogen continues to be excreted in the feces. 

Various methods for distinguishing between the nitrogen of 
feed residues and the nitrogen of excretory products have been 
proposed at different times, but the one which has proved most 
satisfactory and which is generally accepted at present is based 
upon the solubility of the nitrogenous excretory products in 
the solution of pepsin and hydrochloric acid employed in Stut- 
zer's method for the laboratory determination of the digesti- 
bility of protein described in a previous paragraph (162). 

By treatment of a sample of the fresh feces with such a solu- 
tion under proper conditions the excretory nitrogenous products 
are dissolved, and it has been shown that very close agreement 
can be obtained between the artificial and natural digestion of 
protein if the comparison in the latter case be made upon the 
pepsin-insoluble nitrogen of the feces. In other words, the 



120 NUTRITION OF FARM ANIMALS 

pepsin-insoluble nitrogen of the feeds appears quantitatively 
in the feces, where it may be regarded as representing indigesti- 
ble feed protein, while the pepsin-soluble nitrogen of the feces 
is contained in the excretory products, part of which are protein 
(mucus, epithelium, etc.) and part non-protein (residues of 
digestive fluids, etc.). An approximate correction for the 
amount of nitrogenous excretory products may also be com- 
puted by the use of Pfeiffer's factor of 0.4 gram nitrogen per 
100 grams digested dry matter. 

167. Apparent digestibility. — When the results of the or- 
dinary digestion experiment are corrected, in the manner just 
outlined, for the nitrogenous excretory products in the feces 
we get an approximation to the true percentage digestibility 
of the protein, while, as regards the carbohydrates, the error, 
as has been shown, is probably not serious, at least for herbivora. 

There is another way of looking at the matter, ■ however. 
The intestinal products found in the feces are, in effect, part 
of the cost of digesting the feed. They represent the " wear 
and tear " of the digestive organs. The difference, then, be- 
tween feed and feces will show the net gain to the animal from 
the digestion of the feed, that is, it will show how much more 
proteins, carbohydrates, etc., the body has at its disposal than 
it would have had if the feed had not been given. From this 
point of view, we may speak of the digestibility as ordinarily 
determined as the apparent digestibility, and regard it as a 
measure (approximately at least) of the matter gained by the 
body from the consumption of the feed. For many purposes, 
therefore, the apparent digestibility gives a better basis for com- 
paring the values of feeding stuffs than does the real digestibility. 
It was from this point of view that Atwater l proposed the use 
of the term availability as the equivalent of what is here called 
apparent digestibility. 

168. Composition of digested crude fiber. — The crude 
fiber (109) consists of the cellulose of the plant together with 
varying amounts of pentosans and of lignin and other incrusting 
substances, the ratio of which to the cellulose increases with 
the maturity of the plant. Cellulose itself seems to be attacked 
and dissolved with comparative ease by the organisms of the 
rumen and the ccecum, and the same is probably true of the 

1 Rpt. Conn. (Storrs) Expt. Sta., 1897, p. 156. 



DIGESTION AND RESORPTION 1 21 

pentosans, but lignin appears to be much less readily digested 
and some of the other incrusting materials not at all. As a 
consequence, a computation based on the elementary composi- 
tion of the crude fiber of the feed and of the feces respectively 
and on the percentage of the former which is digestible shows 
the digested portion to have approximately the ultimate compo- 
sition and heat of combustion of cellulose. 

This is by no means equivalent to saying that the digested 
crude fiber consists only of cellulose. The variations between 
the results in individual experiments show clearly that this 
cannot be the case and doubtless more or less of the pentosans 
and other ingredients of the crude fiber are attacked to some 
extent, but it is nevertheless evident that the cellulose is the 
chief constituent digested. Neither is the heat of combustion 
of the digested portion in any sense a measure of the energy 
which it can supply for the bodily activities, as will appear 
more clearly later. 

169. Composition of digested nitrogen-free extract. — By 
a difference calculation identical in principle with that em- 
ployed for crude fiber but somewhat more complicated in its 
details and involving certain assumptions, it has been shown 
that the digested portion of the nitrogen-free extract has also 
approximately the composition and heat of combustion of 
starch or cellulose. Even less than in the case of crude fiber 
does this fact serve to fix with any definiteness the nutritive 
value of the digested portion. We know that the nitrogen- 
free extract of feeding stuffs includes a great variety of sub- 
stances (110), some of which, like starch, are digested in the 
narrower sense of the word while many others, like the hemi- 
celluloses, pentosans, etc., are fermented rather than digested. 
The data as to the composition of the digested portion indicate, 
it is true, that it consists chiefly of carbohydrates, but on ac- 
count of the small range of ultimate composition shown by these 
substances no indications are afforded of the specific carbohy- 
drates present. 

170. Digestible carbohydrates. — Since both the digested 
crude fiber and the digested nitrogen-free extract have approxi- 
mately an ultimate composition corresponding to the formula 
C 6 Hi O 5 , it has become customary in estimating the nutritive 
values of feeding stuffs to add together the digestible portions 



122 NUTRITION OF FARM ANIMALS 

of these two groups and to designate the sum as the " digestible 
carbohydrates." The practice dates from the early experi- 
ments of HennebergandStohmann, but in the light of our present 
knowledge has little justification. 

In the first place, as just stated, the agreement in composition 
is but approximate and variable. The essential point, however, 
is that a digestion experiment can show simply that a certain 
amount of material of a certain ultimate composition has failed 
to reappear in the feces of the animal, and by itself affords no 
information as to the changes which it has undergone nor as 
to the nature of the products actually resorbed. As a matter 
of fact, a large share of the " digested " portion of these two 
groups, especially in the case of ruminants, has been fermented 
rather than digested. A considerable proportion of it has been 
excreted in gaseous form as carbon dioxid and methane and 
only a residue of organic acids has been resorbed. Such being 
the case, the term digestible carbohydrates is a palpable mis- 
nomer. 

171. Digested ether extract. — No determinations of the 
composition of the digested ether extract similar to those on 
crude fiber have been made, but a few determinations of the 
heat of combustion of the digested extract are reported by 
Kellner. 1 The presence in the feces of ether soluble excretory 
products (165) interferes with the accuracy of such a comparison 
and its results must be regarded as approximations. The ether 
extract of the feces was found to have a higher heat of combus- 
tion than that of the hay fed, doubtless on account of the 
presence in the former of the indigestible waxes, etc., while 
the computed heat of combustion of the digested portion was 
distinctly lower than that for pure fats, which average about 
9.5 Cals. per gram. The heats of combustion per gram on the 
average of five trials were : — 

Ether extract of hay .... 9.194 Cals. 
Ether extract of feces .... 9.824 Cals. 
Digested ether extract . . . . 8.322 Cals. 

1 Landw. Vers. Stat., 47 (1896), 301. 



CHAPTER IV 
CIRCULATION, RESPIRATION AND EXCRETION 1 

§ i. Circulation 

172. Distribution of nutrients. — The digestive changes by 
which the ingredients of the feed are prepared for the nutrition 
of the organism take place outside the body proper (113). In 
order that the products formed shall serve their purpose they 
must not only be taken up into the body by the processes of 
resorption described in the preceding chapter but they must 
be distributed through it, so that each of its myriad cells may 
receive the substances which it requires. The chief vehicle of 
this distribution is the blood, into which the resorbed nutrients 
are transferred, directly or indirectly, and the distribution is 
accomplished by means of the circulation of the blood, dis- 
covered by Harvey in 1621. 

173. The blood. — This familiar but highly complex fluid 
serves a variety of purposes, being not only the carrier of the 
resorbed feed ingredients to the tissues and cells but transmitting 
to them the equally necessary oxygen and carrying away the 
products of their activity to be used in other parts of the body 
or to be excreted. 

The blood of the higher animals is a thickish, somewhat viscid 
fluid, having a faint but peculiar odor, a slightly salt taste and 
a color varying from bright to dark red. It is somewhat heavier 
than water (sp. gr. 1. 045-1. 07 5), and contains about 21 per 
cent of total solids. Under the microscope it is seen to consist 
of a clear fluid, the plasma, holding in suspension a vast number 
of small, solid bodies, the corpuscles. The latter are of two 
kinds, known as the red corpuscles, or erythrocytes, and the white 
corpuscles, or leucocytes. 

1 Only such a very general consideration of the outlines of these functions as seems 
essential for a proper comprehension of the phenomena of metabolism and of the 
processes of nutrition is attempted here. For a more complete elementary discus- 
sion, the reader is referred to Hough and Sedgwick's The Human Mechanism, 
Chapters IX, X and XI, and for further details to the larger treatises on physiology. 

123 



124 



NUTRITION OF FARM ANIMALS 



174. Red blood corpuscles. — These are by far the more 
numerous of the two kinds. In man they are round like a coin 
but thicker at the edges than in the center, and have a diameter 
of 0.0060-0.0085 millimeter. Their number is enormous, being 
estimated at 4 to 5 J millions per cubic millimeter of blood. 
To them the color and opacity of the blood are due. 

The corpuscles of each species of animal are peculiar to it, both 

as to shape and size, but 
their general characteristics 
are the same in all. Those 
of most animalsaresmaller 
than those of man. Each 
corpuscle is a cell, having 
no nucleus but containing 
as its characteristic ingre- 
dient the conjugated pro- 
tein haemoglobin to which 
the red color of the blood 
is due. Haemoglobin is a 
crystalline substance and 
it has recently been shown 
by Reichert that the 
haemoglobin of each spe- 
cies of animal has its spe- 
cific crystalline form and 
properties. 

175. White blood corpuscles. — The white corpuscles are 
colorless, nucleated cells which are not confined to the 
blood but which, by means of ameboid movements, are able 
to pass through the walls of the blood vessels and the 
lymph spaces of connective tissue as the so-called " wander- 
ing cells." They have important functions, especially in 
protecting the body from disease, but need not be further 
considered here. 

176. Blood platelets. — In addition to the two kinds of cor- 
puscles, the blood contains more minute nucleated cells, rang- 
ing in diameter from 0.0003-0.0005 millimeter, called blood 
platelets, or thrombocytes. They are much more abundant 
than the white corpuscles and are thought to be concerned in 
the coagulation of the blood. 




Fig. 16. — Blood corpuscles. 

Above are shown nine red corpuscles, highly mag- 
nified; below, less highly magnified, the appearance 
of the blood soon after being drawn. (Hough and 
Sedgwick, The Human Mechanism.) 



CIRCULATION, RESPIRATION AND EXCRETION 125 



177. Blood plasma. — This very complex fluid contains, be- 
sides about 90 per cent of water, a great variety of substances, 
the most prominent of which are the proteins, of which two 
groups are recognized, viz., two or more serum globulins and 
the so-called serum albumin, which is probably not a single 
chemical individual. Plasma contains also approximately 
0.1-0.15 per cent of dextrose, from 0.1 to as much as 1.0 per 
cent of fat, usually in some soluble form (243), a great variety 
of so-called extractives which are in part waste products of cell 
action, and about 1 per cent of mineral ingredients. 

178. Coagulation. — When blood is drawn from the body it 
usually coagulates or clots within a few minutes. The coagu- 
lating substance is a globulin called fibrinogen and its coagulation 
is an enzymatic reac- 
tion brought about 
by a ferment, throm- 
bin, believed to be 
derived from the 
blood platelets by 
a very complicated 
process. The coag- 
ulated protein con- 
stitutes the so-called 
blood fibrin, which 
entangles within it- 
self the corpuscles, 
producing the famil- 
iar blood clot. While 
the clot is very bulky 
the dry blood fibrin 
amounts to only 0.2- 
0.3 per cent of the 
weight of the blood. 

179. The heart.— 
Tlje blood is distrib- 
uted to all parts of 
the body by means of 
a most interesting 

organ, the heart, which is in effect a living force pump. 
Figure 17 shows diagrammatically the structure of the mam- 




Fig. 17. — Diagram of mammalian heart. 

a, Left ventricle, b, Right ventricle, c. Left auricle. 
d, Right auricle. /, Aorta. gg, Pulmonary arteries. 
op.. Pulmonary veins. (Smith, Physiology of the Domestic 
Animals.) 



126 NUTRITION OF FARM ANIMALS 

malian heart, which is substantially the -same in all farm 
animals. 

It is divided by an impervious partition into a right and left 
half, and each of these is subdivided by a cross partition into 
two chambers, communicating with each other by a valve in 
the dividing wall. The upper and smaller of these divisions 
are known as the right and left auricles, and the lower and 
larger as the right and left ventricles. Into these cavities of the 
heart open several large blood vessels, whose mouths are closed 
with valves so arranged that the blood can only flow into the 
auricles and out of the ventricles. 

180. Arteries. — The blood vessels which conduct the blood 
from the heart to the various organs of the body are called 
arteries and may be described as tubes with strong, elastic 
and contractile walls, to withstand the force with which the 
blood is pumped into them by the heart. Their walls consist 
of an outer layer of elastic and connective tissue, a middle layer 
of muscular tissue and an inner layer of epithelium. The ar- 
teries originate in the aorta (h, Fig. 18), which receives the blood 
from the left ventricle, and as they extend farther and farther 
from the heart subdivide and throw off branches to the various 
organs, the more minute of which are called arterioles, finally 
ending in the capillaries. 

181. Capillaries. — The capillaries are exceedingly minute 
blood vessels which penetrate all the tissues of the body and 
form the connecting link between the arteries and veins. Their 
walls are thin and delicate, and through them the nutritive mat- 
ters of the blood pass out into the tissues while the waste prod- 
ucts of cell activity pass from the tissues into the blood. In 
Fig. 1 8, n represents the capillaries of the posterior part of the 
body, o those of the stomach and intestines, t those of the kid- 
neys, p those of the liver, and m those of the anterior part of 
the body. The capillaries gradually unite again into larger 
vessels, the veins, which convey the blood back to the heart 
and lungs. g 

182. Veins. — The veins are tubular vessels somewhat similar 
to the arteries but with weaker and non-elastic walls, the pres- 
sure of the blood on them being slight, owing to the interposi- 
tion of the capillaries between them and the arteries and to the 
fact that their total cross section is greater than that of the 



CIRCULATION, RESPIRATION AND EXCRETION 127 



arteries. To prevent any possible flowing back of the blood, 
the veins are provided at intervals with valves which permit the 
blood to pass toward the heart 
but not in the opposite direc- 
tion. The smaller veins unite 
to form larger ones, and finally 
empty their contents through 
two branches into the right 
auricle of the heart. From 
the capillaries of the intestines 
the blood carrying the re- 
sorbed nutrients passes through 
the portal vein, s, to the liver, p, 
is there distributed through 
another system of capillaries 
and then rejoins the blood 
from the extremities through 
the hepatic vein, u. Into the 
branch, k, coming from the 
head and anterior parts of the 
body, the nutrients which are 
resorbed by the lacteals enter 
by way of the thoracic duct. 

183. Course of the blood. — 
The blood returning through 
the veins from the extremities 
of the body to the heart enters 
first the righ't auricle (a, Fig. 
18), through two large veins, 
k and /, coming from the an- 
terior and posterior parts of 
the body. The auricle then 
contracts and the blood, being 
prevented from returning into 
the veins by the valves at their 
mouths, is forced through the 
valve in the partition wall into 
the right ventricle, b. This, 
in turn, contracting, the blood, prevented as before by a 
valve from turning back in its course, is forced out of the 




Fig. 18. — Scheme of circulation of 
blood. (Armsby, Manual of Cattle 
Feeding.) 



128 NUTRITION OF FARM ANIMALS 

ventricle into the pulmonary artery, c, which divides into two 
branches leading to the capillaries of the right and left lungs, 
d, d. The entrance to this blood vessel, like that of the others, 
is provided with a valve which prevents the return of the blood. 
The blood, after passing through the lung capillaries, returns 
to the left auricle, /, through the pulmonary veins, represented 
by e. The auricle then contracting, sends the blood into the^ 
left ventricle, g, which, in its turn, contracts powerfully and 
expels the blood into one -large vessel, the aorta, h. The aorta, 
soon after leaving the heart, divides into two branches, i and j, 
and these repeatedly subdivide, forming the arteries which carry 
the blood to the arterioles and capillaries, whence it returns 
again through the veins to the right side of the heart. 

The passage of the blood from the left side of the heart through 
the body capillaries and back to the right side is called the 
greater or systemic circulation ; that from the right side 
of the heart through the lung capillaries, the pulmonary cir- 
culation. 

The appearance of the blood in the veins and arteries is 
strikingly different. In the veins it has a dark, cherry-red 
color, but after it has passed through the lungs and is sent out 
by the heart to the arteries it has a bright scarlet color. The 
former is called venous, the latter, arterial blood. An exception 
to this rule, that the arteries carry bright red blood and 
the veins dark, is found in the pulmonary circulation, where, 
of course, the vessels leading from the heart to the lungs carry 
venous blood, and those leading from the lungs to the heart, 
arterial. Nevertheless, the general nomenclature is adhered 
to, and the former are called arteries and the latter veins. Ar- 
teries conduct the blood from the heart, veins toward it. 

184. Mechanics of circulation. — While it is not uncommon 
to speak of the flow of the blood, or of the blood stream, sug- 
gesting an analogy to a brook or river, the circulation is not in 
reality a flow of this sort but resembles rather the movement of 
the water pumped into a hose by a force pump. The heart 
constitutes the force pump and the arteries correspond to the 
hose. The powerful muscular contraction of the ventricle 
drives the blood into the arteries by successive impulses, as the 
water is driven into the hose by the pump. If the end of the 
hose were left open the water would issue in a series of spurts 



CIRCULATION, RESPIRATION AND EXCRETION 129 

corresponding to the strokes of the pump. By the addition of 
a nozzle of smaller diameter than the hose this intermittent 
outflow is converted into a steady stream. The resistance of 
the nozzle to the passage of the water gives rise to a pressure 
which stretches the walls of the hose, and their elastic force 
maintains the flow between the strokes of the pump. 

Substantially the same conditions exist in the body. The 
walls of the arteries are elastic while the capillaries in which 
the arteries terminate may be compared to the nozzle of the hose. 
The resistance caused to the flow of the blood by these minute 
channels tends to hold it back and produces a pressure in the 
arteries which, like the pressure in the hose, causes a steady 
movement of blood through the capillaries. In other words, 
the immediate cause of the motion of the blood through the 
capillaries is the elasticity of the arterial walls. If the latter 
become weakened and lose their tone or become hardened as in 
old age (arteriosclerosis), the driving force is lessened and the 
circulation slows down, since the veins can return blood to the 
heart only as fast as it is forced through the capillaries by the 
arterial pressure. The blood pressure in the arteries, therefore, 
is an important indicator of the activity of the circulatory sys- 
tem. The veins serve substantially as a return system, the 
blood being pushed along them by the residual pressure from the 
capillaries, perhaps aided somewhat by the expansion of the 
auricle of the heart, while valves prevent any backward flow. 
As compared with the arterial pressure, therefore, the blood 
pressure in the veins is low. 

185. The lymph. — The body cells are not closely packed to- 
gether but are imbedded more or less loosely in connective tis- 
sue (83) leaving spaces between them (intercellular spaces). 
These spaces contain a colorless transparent fluid called the 
lymph which is the real nutritive medium in which the cells 
live. From it, by means of osmosis through their outer mem- 
branes and perhaps in other ways, the cells derive the substances 
required for their vital activities and into it they discharge 
the waste products of their action. 

The lymph in its turn stands in relation to the blood, from 
which it is separated by the thin walls of the capillaries. While 
the minute capillaries penetrate all the tissues and convey blood 
to all parts of the body, it should be understood that the cir- 



13° 



NUTRITION OF FARM ANIMALS 



culatory apparatus is a closed system. Even the very thin 
delicate walls of the capillaries are continuous and the blood 
does not come into direct contact with the living cells, except, 
of course, those lining the blood vessels. The accompanying 
diagram (Fig. 19) illustrates schematically the anatomical re- 
lations of the cells, intercellular spaces, capillaries and lym- 
phatics, A representing a minute artery, or arteriole, subdi- 
viding into capillaries which are reunited to form the small 
vein V. Through the capillary walls the nutritive substances 
contained in the blood pass, partly by osmosis and partly by 




Fig. 19. — Relation of cells to blood vessels and lymphatics. (Hough and 
Sedgwick, The Human Mechanism.) 

filtration, into the lymph to maintain its stock, while the waste 
products of cell action pass in the opposite direction into the 
blood and are carried off. 

186. Lymphatics. — In the intercellular spaces there orig- 
inates another set of minute vessels, the lymphatics, which 
unite like the capillaries to form larger ones (L in Fig. 19) and 
finally form two main lymphatic trunks, the thoracic duct 
and the small lymphatic trunk, which empty into the great veins 
near the heart. The lacteals of the intestinal villi, through which 
the fats are chiefly resorbed, belong to the lymphatic system. 



CIRCULATION, RESPIRATION AND EXCRETION 131 



In the lymphatics there is a continuous slow movement of the 
lymph from the tissues towards the main trunks, the lymphatics, 
like the veins, being provided at intervals with valves prevent- 
ing a backward flow. This lymph 
flow is sustained in part by a 
slightly greater pressure in the 
lymphatic spaces but largely by 
the rhythmic motions of breath- 
ing, and is aided by muscular 
activity. Thus, in addition to the 
exchange of substances between 
the lymph and the blood through 
the walls of the capillaries, there 
is a general movement of the 
lymph itself over the surface of 
the cells which tends to facilitate 
the exchanges between it and the 
protoplasm. 

187. Adjustment of circula- 
tion. — The activity of the various 
tissues varies at different times. 
A muscle, for example, is some- 
times at rest and sometimes 
actively contracting. Conse- 
quently, a greater or less supply 
of food material and of oxygen will 
suffice according to circumstances, 
and the blood supply needs to be 
regulated accordingly. 

This regulation is effected in 
substantially two ways. First, 
when the cells of any particular 
tissue increase their activity they 
consume more oxygen and give 

rr 1^11 Fig. 20. — Main lymphatic trunks 

off more waste products than be- (in white) . (Ho ugh and Sedgwick, 
fore, tending to produce a relative The Human Mechanism.) 

deficiency of the one and an ex- 
cess of the other in the lymph and blood. These conditions 
bring about an increase in the heart action (194), probably 
by means of a nerve stimulus, so that the amount of blood 




132 NUTRITION OF FARM ANIMALS 

passing through the heart is increased and a more abundant 
supply of it reaches the active tissues. Second, there may 
be a partial shunting of the blood supply from one region 
of the body to another as one set of organs or another calls 
for a larger amount. This is accomplished through the agency 
of the middle or muscular coat of the arterioles, controlled by 
the so-called vaso-motor nerves. When a larger supply of blood 
is called for in the muscles, for example, these fibers relax and 
allow the arterioles to enlarge, thus reducing the resistance 
offered to the blood flow and allowing the arterial pressure to 
force blood into the capillaries more rapidly. To compensate 
for this there is a contraction of the arterioles of the internal 
organs, especially of the abdominal organs, resulting in a di- 
minished blood supply. The effect of the performance of work 
upon digestion, discussed in Chapter XVI (721), is possibly 
connected with this effect upon the blood flow. On the other 
hand, after a hearty meal the arterioles of the digestive tract 
relax, while the superficial blood vessels tend to contract and 
the blood supply is partially diverted from the surface tissues 
to the internal organs. This power of the body to regulate 
the supply of blood to different regions is of special importance, 
as will appear later (321), in connection with the regulation of 
the body temperature. 

§ 2. Respiration 

188. The oxygen supply. — By means of the processes 
described in the preceding section the nutritive materials de- 
rived from the feed and taken up by the intestinal capillaries 
and lacteals are distributed to the various tissues and cells. 
Equally necessary with a supply of feed materials to the living 
cells, however, is a supply of oxygen, and this another set of or- 
gans, those of respiration, are engaged in furnishing to the blood 
through another set of capillaries for transmission to the cells. 

189. The lungs. — The transfer of oxygen from the air to the 
blood is effected in the lungs, which, with the heart and large 
blood vessels, fill the cavity of the thorax, or chest. This cav- 
ity is enclosed on the sides by the ribs and their connections, 
forming the chest walls, and is separated from the abdominal 
cavity, containing the digestive organs, by a strong, arched, mus- 



CIRCULATION, RESPIRATION AND EXCRETION 133 



cular partition, convex toward the 
chest, the diaphragm. The air 
enters the lungs through the 
trachea, or windpipe, from the 
mouth and nostrils. The trachea, 
after reaching the chest, divides 
into two branches, or bronchi, 
one leading to the right and one 
to the left lung. Each bronchus 
subdivides repeatedly into a 
multitude of fine tubes, the 
smallest of which are called bron- 
chioles (little bronchi), each of 
which finally ends in an alveolus, 
the inner surface of which is much 
increased by being arranged in 
the form of pits or air cells. 
In Fig. 21, c represents a bronchiolus, aa two alveoli and bb 
the air cells. Figure 22 shows diagrammatically on a large 
scale a cross section of two alveoli. 




Fig. 21. — Alveoli of lung. (Wil- 
ckens, Form und Leben der Land- 
wirthschaftlichen Hausthiere.) 




Fig. 22. — Section of two alveoli. (Hough and Sedgwick, The Human 

Mechanism.) 



134 NUTRITION OF FARM ANIMALS 

The walls of the trachea and bronchi consist of cartilaginous 
rings which prevent them from collapsing. The alveoli and 
bronchioles are surrounded and bound together by connective 
tissue consisting largely of elastic fibers so that the minute air 
cavities of the lungs are extensible and their walls elastic. In 
this connective tissue are found the larger branches of the 
pulmonary artery and pulmonary vein, connected by a net- 
work of capillaries which are spread out over the inside of the 
alveoli in direct contact with their lining membrane. Each 
lung is enclosed in a double-walled sack, the pleura, one wall 
of which covers the lungs and the other the chest walls and 
diaphragm, the narrow cavity between the two being filled 
with a liquid. 

190. Mechanics of breathing. — In breathing, the lungs 
themselves play an essentially passive role, the movement of 
air into and out of them being effected by changes in the capac- 
ity of the chest brought about by the movements of the dia- 
phragm and ribs. 

Since the diaphragm is convex toward the chest its contrac- 
tion tends to pull the apex of the dome toward the abdomen, 
thus increasing the volume of the chest cavity and by pressure 
on the digestive organs distending the abdominal walls. When 
the diaphragm relaxes again the volume of the chest is reduced 
and the abdominal walls return to their former position. This 
type of breathing is what is called abdominal breathing. 

The ribs pass obliquely around the chest from the spine to 
the breast bone (sternum). By means of the intercostal 
muscles, located between them, the ribs can be elevated, 
turning on their attachments to the spine and sternum, thus 
increasing the diameter of the chest both from side to side 
and from front to back and so increasing the capacity of the 
chest cavity. This type of breathing is called costal, or rib, 
breathing. 

The two types of breathing are ordinarily combined. By 
their joint action the size of the closed pleural cavity contain- 
ing the lungs is increased and the atmospheric pressure forces 
more air into the extensible alveoli of the lungs, so that the 
latter expand along with the chest cavity, the whole constitut- 
ing the act of inspiration, or breathing in. When the dia- 
phragm and the intercostal muscles relax, the elasticity of the 



CIRCULATION, RESPIRATION AND EXCRETION 135 

chest walls causes them to return to their original position and 
this, together with the elasticity of the lung tissue itself, com- 
presses the air in the alveoli and forces part of it out through 
the trachea, this constituting the movement of expiration. 

Inspiration is an active process, while expiration is chiefly 
passive. The respiratory movements are ordinarily what are 
called involuntary, i.e., they go on independent of conscious- 
ness, being governed by automatic nerve impulses, conveyed 
by nerves of various origin but controlled by the so-called " res- 
piratory center," although the movements can be accelerated 
or retarded or even suspended entirely for a few moments by 
an effort of the will. 

From the foregoing, it is plain that the ventilation of the 
lungs does not consist in the passage of air through them but of 
a surging or tidal movement in and out. The alveoli are never 
entirely emptied of air even in forced expiration. In inspiration 
the new or tidal air enters the trachea and bronchi, gives up by 
diffusion some of its oxygen to the residual air in the alveoli 
and receives from the latter some of the carbon dioxid which 
it contains. In this way, by the ebb and flow of the tidal air 
and by diffusion between it and the residual air, fresh oxygen 
is being continually introduced into the lungs and carbon 
dioxid continually removed. 

191. Absorption of oxygen. — The oxygen introduced into 
the alveoli of the lungs in the manner just described is still 
outside the body proper, just as is the feed in the digestive 
tract. In order to fulfill its functions it, like the feed, must be 
transmitted to the blood for distribution to the tissues. This 
transfer is accomplished in the lung capillaries as is that of the 
feed in the intestinal capillaries. In the lung capillaries the 
blood is separated from the air of the alveoli only by a thin mem- 
brane. The coloring matter of the red corpuscles, haemoglobin, 
has the power of entering into combination with oxygen, of 
which it can take up a maximum of about 1.66 c.c. per gram, 
forming a loose chemical compound known as oxy haemoglobin. 
The red corpuscles of the venous blood as it comes to the lungs 
contain chiefly haemoglobin. In their passage through the 
lung capillaries they are exposed to the oxygen of the alveolar 
air and, aided by the relatively large surface of the blood cor- 
puscles, their haemoglobin takes up more or less oxygen and is 



136 NUTRITION OF FARM ANIMALS 

converted partly or wholly into oxyhemoglobin, the amount 
of the oxygen taken up ranging from eight to twelve volume 
per cent. The color of haemoglobin is a dark red or purplish, 
while that of oxyhemoglobin is bright scarlet. To this differ- 
ence of color is due the marked difference in appearance be- 
tween venous and arterial blood. 

192. Respiration of tissues. — The term respiration is very 
commonly applied to the mechanical processes of breathing 
just described or to the exchange of gases in the lungs. In 
reality all these are preliminary to the real respiration, which 
takes place in the tissues. The vital processes in the body 
cells consist, broadly speaking, as will appear in detail in the 
next chapter, of a series of oxidations. The requisite oxygen 
is necessarily drawn from the lymph in which the cells exist (185), 
while the carbon dioxid produced by oxidation is discharged 
into it. The lymph, therefore, tends continually to become 
richer in carbon dioxid and poorer in oxygen. In the manner 
just described the blood takes up oxygen in the lungs and acts 
as a carrier through the body. Through the capillary blood 
vessels of the body generally, therefore, there are continually 
passing red blood corpuscles charged with loosely combined 
oxygen, while on the other side of the capillary wall is a fluid 
(the lymph) in which the partial pressure of oxygen is relatively 
low. Accordingly, the combination of oxygen and haemoglo- 
bin is dissociated to a greater or less extent and oxygen passes 
into the lymph as required to supply the needs of the cells. At 
the same time the excess of carbon dioxid in the lymph passes 
in the opposite direction into the blood and is thus removed 
from the neighborhood of the cell. 1 It is this continual con- 
sumption of oxygen and elimination of carbon dioxid by the 
cells which constitutes the real act of respiration, while the 
complex structure of the lungs and the elaborate mechanism of 
breathing and of the blood corpuscles are simply means for 
providing oxygen to the cells and taking away carbon dioxid. 
That the movements of breathing are not an essential part of 
respiration is strikingly shown by the fact that it is perfectly 
possible by suitable devices to maintain oxygenation of the blood 

1 In these exchanges, as in other similar ones, while diffusion doubtless plays a 
large part, its effects are no doubt modified by the special properties of the living 
cells. 



CIRCULATION, RESPIRATION AND EXCRETION 137 

of an animal in the absence of any respiratory movements what- 
ever. 

193. Respiration regulated by cell activity. — It is apparent 
from the foregoing that the amount of oxygen taken up by the 
blood in the lungs depends in the first instance upon the amount 
of this element consumed by the body cells. When they are 
relatively inactive they take up correspondingly little oxygen 
from the lymph and the tension of oxygen in the latter is low- 
ered but little. As a consequence there is less dissociation of 
the oxyhemoglobin in the blood and the corpuscles tend to 
return to the lungs still carrying more or less oxygen and there- 
fore capable of taking up relatively less. On the other hand, as 
the tissues become more active they consume more oxygen, the 
oxyhemoglobin in the corpuscles is more extensively dissociated 
and the corpuscles tend to come back to the lungs relatively 
exhausted of oxygen and ready to take up the maximum amount. 

Any considerable degree of tissue activity, however, calls for 
a more rapid supply of oxygen than can be provided for in this 
way and this need is met by a nerve stimulus to the heart, caus- 
ing it to beat faster and more powerfully, thus increasing the 
arterial pressure and therefore the amount of blood passing 
through the capillaries in a given time. In these two ways 
the amount of oxygen absorbed in the lungs is very accurately 
adjusted to the needs of the organism. It is impossible to 
stimulate the body oxidations by a free supply of air as, for 
example, by deep and rapid breathing, as one might blow up a 
fire with a bellows, or to get more intense combustion by re- 
placing air with pure oxygen. In the body such additional air 
or oxygen never reaches the fire. Each corpuscle is a recep- 
tacle which can carry only a definite amount of oxygen and if 
it comes back to the source still partly filled it takes up so much 
the less on its next trip, or if it travels slowly it is less efficient 
than if it returns more frequently. The respiration of the 
tissues can no more be affected by increasing the ventilation of 
the lungs than the amount of water delivered by a pump is by 
the volume of the stream from which the water is taken. 

194. Regulation of the rhythm of breathing. — The illusr 
tration just used is true, of course, only on the condition that 
the stream carries at least as much water as the pump can 
handle. So, too, the amount of oxygen available in the lungs 



138 NUTRITION OF FA*RM ANIMALS 

must at least equal the amount required by the tissues. It is 
a familiar observation that the rate of ventilation of the lungs 
varies with the varying activity of the body cells. This is 
true of all these activities, but is most familiar in the case of 
muscular work which, as everyone knows, promptly increases 
the rate and depth of breathing, so that severe exercise, such as 
rapid running, for example, brings into play all the reserve re- 
sources of the breathing mechanism. As already stated 
(190), the muscles which are used in breathing are ordinarily 
controlled from the so-called " respiratory center " and it is 
through this center that the regulation is effected. If, for 
example, an animal be supplied with air largely diluted with 
some indifferent gas, such as nitrogen or hydrogen, the partial 
pressure of the oxygen in the alveoli is so reduced that the hae- 
moglobin of the blood is only partially saturated with oxygen. 
Such a deficiency of oxygen stimulates the respiratory center 
and produces more active breathing and a corresponding in- 
crease in the rapidity with which the air in the alveoli (residual 
air) is renewed. 

Under ordinary conditions, however, the stimulus to the 
respiratory center is not a lack of oxygen in the blood but an 
excess of carbon dioxid. As has already been implied, the 
lungs serve not only for the absorption of oxygen but for the 
elimination of the carbon dioxid produced by respiration, 
which passes by way of the lymph to the blood and thence to 
the air in the alveoli of the lungs. Any increase in the ac- 
tivity of the tissues by which more carbon dioxid is produced 
tends to increase the content of this substance in the blood. 
Even a very slight increase, however, promptly stimulates the 
respiratory center and so causes greater activity of the muscles 
concerned, resulting especially in deeper and to some extent more 
rapid breathing. By this means the ventilation of the lungs 
is augmented and so provision is made for the removal of a 
greater amount of carbon dioxid. 

It is plain, however, that a simple increase in the lung ven- 
tilation alone is not sufficient, except in a limited degree, to carry 
away more carbon dioxid from the tissues. Along with the 
increased ventilation there must be an increase in the rapidity 
of the blood current which is the medium by which the transfer of 
gases between the lungs and the lymph takes place. Accordingly, 



CIRCULATION, RESPIRATION AND EXCRETION 139 

we find that substantially the same stimuli which cause more 
active breathing also stimulate the heart action and vice versa. 
Lack of oxygen or excess of carbon dioxid are the two prin- 
cipal factors in regulating the breathing rhythm but by no means 
the only ones. They are, however, the ones of most impor- 
tance in the present connection. 

195. Gaseous exchange through the skin. — In addition to 
the exchange of gases between the air and the blood which 
goes on in the lungs, a similar process takes place, though to a 
much smaller extent, through the skin. The true skin, under- 
lying the cuticle or scarf-skin, is penetrated by capillary blood 
vessels, and in its passage through these capillaries the blood 
gives off some carbon dioxid and takes up some oxygen by dif- 
fusion through the skin. The amounts given off and taken 
up are small compared with the corresponding amounts in the 
lungs, but still are not inconsiderable, and must be taken into 
account in accurate experimental work. 

§ 3. Excretion 

196. Excretory products. — As already implied, the vital 
activities of the body cells lead to the formation of products 
which must be removed from the cells and some of which must 
ultimately be discharged from the body. The next chapter 
will be concerned with the nature of the more important of 
these products and with some of the steps by which they are 
formed. For the present, it suffices to say that the gradual 
oxidations of non-nitrogenous material taking place in the cells 
give rise substantially to the production of carbon dioxid and 
water, while the proteins and related substances yield in addition 
certain comparatively simple nitrogenous substances of which 
the most abundant is urea. In addition to these substances, 
more or less of the mineral ingredients also pass into the excreta. 

197. Excretion of carbon dioxid. — As stated in the previous 
section, the carbon dioxid produced by the tissue respiration 
passes by way of the lymph into the blood and is excreted 
through the lungs and to a minor degree through the skin. In 
the blood the carbon dioxid is carried by both the corpuscles 
and the plasma, but chiefly (two-thirds or more) by the latter, 
in combination with proteins and haemoglobins, but especially 



140 NUTRITION OF FARM ANIMALS 

with the alkalies. As in the case of oxygen, the amount of 
carbon dioxid contained in the blood depends upon the partial 
pressure of this gas in the surrounding medium. Since the ten- 
sion of the carbon dioxid in the alveolar air is less than that in 
the blood of the alveolar capillaries, the carbon dioxid passes 
from the latter to the former.. If the air were stationary the 
process would continue until an equilibrium was reached. 
Since the air is being continually renewed by breathing, the 
tension of carbon dioxid in it is kept permanently lower than 
that in the blood and there is, therefore, a continual passage of 
carbon dioxid from the blood to the alveolar air. 

It is by means of this tendency to equilibrium that the mech- 
anism for the regulation of breathing is set in motion. In- 
creased tissue respiration discharges more carbon dioxid into the 
blood, where its tension increases. This causes a more rapid 
diffusion of the gas into the alveolar air and tends to raise its 
carbon dioxid tension also, so that with an unchanged rate of 
lung ventilation the carbon dioxid level of both the alveolar 
air and the blood would be raised. Even a very slight rise in 
the carbon dioxid tension in the blood, however, as already 
stated, acts promptly upon the respiratory center and stimu- 
lates the muscles of breathing, resulting in an increased lung 
ventilation and consequently a more rapid excretion. At the 
same time the rapidity of circulation is increased and in these 
two ways the level of carbon dioxid tension in the blood and 
in the alveolar air is maintained very constant. On the other 
hand, if the lung ventilation be artificially increased, as by 
artificial respiration or by the use of oxygen, the carbon dioxid 
excretion may be so facilitated that the amount in the blood 
falls below the normal and the movements of breathing may be 
temporarily suspended (apncea). 

198. Excretion of nitrogenous products. — The urea and 
other nitrogenous products of cell action, like the non-nitrog- 
enous products, pass ultimately into the blood. In its course 
through the body the blood passes through a capillary system 
in two bean-shaped organs, the kidneys, indicated by / in Fig. 
1 8, situated in the abdominal cavity on either side of the spine 
near the loins. In these organs the urine is being continually 
secreted, passing thence through the ureters into the bladder 
from whence it is voided at intervals. 



CIRCULATION, RESPIRATION AND EXCRETION 141 

The chief stimulus to the secretion of water by the kidneys 
is the water content of the blood, the kidneys acting as regu- 
lators of this important factor and eliminating more or less water 
as the blood contains a larger or smaller percentage of it. 

As regards the excretion of dissolved matter, very interesting 
relations exist. With one important exception (hippuric acid) 
the kidneys do not manufacture the excretory products. Their 
essential function is to maintain the composition of the blood 
constant. For each substance capable of being excreted at all 
in the urine there exists a certain minimum concentration in 
the blood above which it begins to pass through the kidneys into 
the urine. For the normal excretory products, as well as for 
foreign substances, this minimum approaches zero, that is, only 
very minute amounts of these substances can be retained in 
the blood. For dextrose the limit is approximately 0-2-0-3 
per cent, for sodium chlorid o-6 per cent, etc. So long as 
the percentage of one of these substances in the blood does not 
exceed its own particular limit, none of it is excreted through the 
kidneys. On the other hand, a slight rise above this limit 
causes an excretion of the substance concerned. This function 
of the kidneys has been likened to the working of an overflow 
valve on a tank. It should be added that each particular sub- 
stance has its own minimum,. independent to a large degree of 
all the others. 

The functions of the kidneys, however, in this respect are 
not so simple as those of an overflow valve for the reason that 
the concentration of the excreted substances is greater in the 
urine than in the blood. In other words, the kidney does its 
work by transferring substances from a fluid of lower to a fluid 
of higher osmotic pressure and the expenditure of energy in 
this work is not inconsiderable. This is notably true of urea 
and the other nitrogenous waste products, of which only traces 
can be detected in the blood. 

In addition to the nitrogenous substances excreted in the 
urine there are present in the feces, as already noted (154), 
excretory products which represent a certain fraction of the 
organic body waste. Finally, small amounts of urea and 
other nitrogenous substances are excreted in the perspiration. 

199. Excretion of ash ingredients. — Being non-volatile 
the ash ingredients are excreted chiefly through the feces or 



142 NUTRITION OF FARM ANIMALS 

urine according as the intestines or kidneys form the normal 
path of excretion, although they are contained to a small ex- 
tent also in the perspiration. 

The intestines are the usual path of excretion for certain 
mineral substances, notably iron, calcium and to some extent 
magnesium. To these must be added in the case of the her- 
bivora phosphoric acid, which, under ordinary conditions, is 
excreted in the feces. The urine of herbivora, especially when 
they consume roughage freely, or in more general terms when 
the basic predominate over the acid ingredients of the ash, is 
alkaline and contains but minute amounts of phosphoric acid. 
On the other hand, during fasting or upon a ration having an 
acid ash, the urine may have an acid reaction and then, like the 
acid urine of carnivora or omnivora, may contain phosphoric 
acid. The urine is the normal vehicle for the excretion of 
sulphur, chlorin and the alkalies. 

200. Excretion of water. — The motions of air in and out of 
the lungs are the means of removing from the body more or 
less incidentally large amounts of water by simple evapora- 
tion. The presence of water vapor in the expired air is a fa- 
miliar fact, shown by its condensation on a cold surface or in 
cold air. The skin likewise acts, by means of its sweat-glands, 
as a channel for the removal of water from the system, con- 
siderable being continually evaporating from the skin in the 
form of the " insensible perspiration." Under certain circum- 
stances the excretion of water is so rapid as to give rise to the 
formation of visible drops (sweating). 

The amounts of water excreted in these two ways are larger 
than are sometimes realized. For example, a thousand pound 
ox at ordinary temperature and on light feed may easily ex- 
crete through the lungs and skin eight to ten pounds of water 
in twenty-four hours, the amount depending to a considerable 
extent upon the temperature and amount of movement of the 
surrounding air. The feces also contain a large percentage of 
water and in the case of herbivorous animals the amount thus 
eliminated is very considerable. 

Finally, water is excreted in the urine, serving as a solvent 
for the nitrogenous products of cell activity which are removed 
through this channel. The amount of water thus excreted de- 
pends in part upon the amount consumed, in part upon the 



CIRCULATION, RESPIRATION AND EXCRETION 143 

quantity of nitrogenous material which must be dissolved and 
in part upon the amount eliminated through the lungs and 
skin. 

Most of the water excreted by animals is, of course, con- 
sumed as such, but it includes also that formed by the oxida- 
tion of organic hydrogen — the so-called metabolic water. 
Babcock has shown that in some classes of animals, notably 
insects, this metabolic water suffices for all the needs of the 
organism, so that they are not dependent upon a supply of 
drinking water. 



CHAPTER V 
METABOLISM 

§ i. General Conception 

201. Assimilation and excretion. — The cell has already been 
defined (73) as the biological unit of life. It is the living proto- 
plasm of the body cells which is the seat of the multifarious 
activities of the organism. 

Every such activity requires an expenditure of energy, de- 
rived from the breaking down of constituents of the proto- 
plasm itself or of cell enclosures and solutes and their transfor- 
mation into other forms. The presence of oxygen is essential 
to these changes and while, as will appear, they seldom are 
primarily direct oxidations, nevertheless, they yield products 
which are ultimately oxidized to carbon dioxid, water and 
other comparatively simple compounds. 

Two things, then, are necessary for the continued life of the 
cell : first, a supply of material from without to replace that 
consumed and, second, the removal of the waste products of 
its activities. Both conditions are fulfilled in the higher ani- 
mals by the circulation of the blood and lymph. In the pro- 
cesses of digestion, the heterogeneous nutritive materials con- 
tained in the feed are gradually brought into solution by a series 
of molecular cleavages, so that the resorptive organs transmit 
to the blood and lymph current a qualitatively uniform material 
consisting of substances of comparatively simple molecular 
structure (146, 147), while oxygen is supplied to the blood cor- 
puscles through the lung capillaries. The mechanism of cir- 
culation is continually distributing to each tissue and cell oxygen 
from the lungs and nutritive material from the digestive tract 
and carrying away the waste products of cell action to the 
various organs of excretion which remove them from the body. 

202. Definition of metabolism. — It is clear from the fore- 
going that the body is the seat of extensive chemical trans- 

144 



METABOLISM 



HS 



formations. On the one hand, molecules of resorbed digestion 
products are being assimilated by the body cells and built up 
into the structure of their protoplasm, while, on the other 
hand, molecules of protoplasm or of cell enclosures are being 
broken down and oxidized, yielding finally the relatively simple 
excretory products. 

The term metabolism is commonly used to designate the to- 
tality of the chemical changes which the constituents of the 
resorbed feed undergo in the course of their conversion into 
the corresponding excretory products. Similarly, one may 
speak in a more restricted sense of the metabolism of single 
ingredients of the feed, as of the proteins, carbohydrates or 
fats, protein metabolism, for example, signifying the chemical 
changes undergone by the digestion products of the proteins 
of the feed during their assimilation and subsequent transfor- 
mation into excretory products. The adjective metabolic is 
also used to describe these chemical changes. 

203. Anabolism and katabolism. — The term metabolism, 
as just defined, includes processes of two distinct kinds, viz., 
those by which molecules of sugars, organic acids, amino acids, 
etc., are built up into more complex compounds in the body 
and those by which these complex compounds are broken down 
again into simpler substances and finally into the excretory 
products. 

The building up metabolism has received the name anabolism, 
while the breaking down or oxidative phase is called katabolism. 
Any change in the direction of greater molecular complexity 
is spoken of as an anabolic change, while one in the direction of 
greater molecular simplicity is a katabolic change. 

It must not be inferred from what has been said that anabolism 
always precedes katabolism. Neither is the breaking down of cell 
constituents by any means a process of uninterrupted katabolism. 
On the contrary, many instances are known in which it is interrupted 
at various stages by anabolic changes of one sort or another. While 
the general direction of the change is towards simplification, there 
are eddies in the current. Moreover, it is by no means probable that 
all the resorbed substances are actually built up into protoplasm 
before being katabolized. It is true that, to the best of our knowl- 
edge, the metabolic processes take place within the cells but it ap- 
pears unlikely that the relatively large amounts of material some- 



146 NUTRITION OF FARM ANIMALS 

times katabolized must first become integral parts of the protoplasm. 
In other words, it is probable that the cells have the power to katab- 
olize substances present within them but not structurally a part of 
them. 

204. Synthetic processes in the body. — The foregoing conception 
of metabolism implies that the body has power to carry out extensive 
chemical syntheses, contrary to the idea still current that the course 
of chemical change in the organic world is toward the building up of 
complex compounds in the plant and their breaking down to simpler 
ones in the animal. Synthethic chemical changes were long regarded 
as peculiar to the vegetable kingdom, while the reactions in the ani- 
mal body were supposed to be exclusively analytic. The first syn- 
thetic action to be recognized in the animal was the formation of 
hippuric acid from benzoic acid, discovered by Keller and Wohler in 
1824, and which attracted wide attention. More recent physio- 
logical investigations have shown that this is by no means an isolated 
case, but that syntheses in great variety are executed in the animal 
body. No such sharp distinction between animal and vegetable 
organisms exists as was formerly supposed. The fundamental laws 
of metabolism are the same for both and both execute synthetic as 
well as analytic processes. It is only the special synthetic activity 
of the chlorophyl in green plants which tends to obscure this funda- 
mental likeness. The conception, then, that the digestive cleavages 
supply to the body cells comparatively simple "building stones" 
which are synthesized to produce the complex ingredients of cells 
and tissues is quite in harmony with our general knowledge of the 
nature of metabolism. 

205. Metabolism oxidative and analytic. — Metabolism re- 
garded as a whole may be characterized chemically as an oxi- 
dation. Oxygen is introduced into the system through the 
blood and reacts with the feed or tissue materials or with the 
products of their breaking down, and the final excretory products 
are either completely oxidized substances, like carbon dioxid 
and water, or substances approaching this condition, like 
urea, etc. 

From a slightly different point of view, metabolism as a whole 
may be characterized as an analytic as opposed to a synthetic 
process. The general tendency is toward the formation of 
simpler molecules. For example, the molecule of dextrose or 
levulose contains 24 atoms and those of the three most com- 
mon fats, respectively, 155, 167 and 173 atoms, while the 
molecules of carbon dioxid and water resulting from their me tab- 



METABOLISM 147 

olism contain but 3 atoms each. Even the cleavage products 
of protein which are resorbed from the digestive tract are, with 
few exceptions, much more complex than the final products 
which result from their metabolism. 

206. Metabolism a gradual process. — While metabolism 
has just been characterized as an oxidative process, and is often 
loosely spoken of as a burning of the feed or tissue ingredients, 
it is in fact radically different from what is commonly under- 
stood by these terms. The building up and breaking down of 
materials in metabolism is a gradual, i.e., a step by step, process. 

Metabolism is the sum of the chemical reactions through which 
the life of the cells is manifested. These reactions, however, 
differ from tissue to tissue and from cell to cell, and even in the 
same cell from time to time, and the resulting products are 
correspondingly numerous and varied. Between the nutrients 
supplied to the cells by the blood and the final products of 
metabolism as excreted from the body there are innumerable 
intermediate products, comparatively few of which, in all proba- 
bility, have been recognized. We know the first and last terms 
of the series and thus are able to measure, as it were, the alge- 
braic sum of the changes, but of the single factors making up 
the so-called intermediary metabolism as well as of the specific 
tissues concerned in the changes, we are largely ignorant, al- 
though we know that they are numerous. 

Furthermore, while metabolism results in the formation of 
highly oxidized products, it does not consist primarily in the 
direct union of oxygen with feed materials, i.e., the step by 
step processes of which it is made up do not consist of a series 
of partial oxidations. The primary processes of metabolism 
are of the nature of cleavages and hydrations and it is only 
the comparatively simple molecules resulting from these which 
unite directly with oxygen. Correspondingly, the extent of 
metabolism is determined by the amount of functional activity 
of the various cells and not, as in the case of direct oxidation 
in a fire, by the supply of oxygen (193) . The somewhat com- 
mon notion that an increased proportion of oxygen in the air or a 
voluntary increase in the rate and depth of breathing may cause 
more material to be oxidized in the body is without foundation, 
except so far as increased breathing involves increased mus- 
cular exertion. 



148 NUTRITION OF FARM ANIMALS 

207. Purpose of metabolism. — As implied at the opening 
of this chapter, the vital activities of the body are essentially 
transformations of energy. The living body is continually 
doing work upon its surroundings and continually loosing heat 
to them and the energy for the production of work and the main- 
tenance of the body temperature is derived, as already stated, 
from the transformation of the chemical energy contained in 
the substances broken down, this transformation being indeed 
the essence of the whole process. This fact is familiarly, if not 
altogether accurately, expressed in the statement that the 
feed is the fuel of the body. 

There will be occasion later to consider this aspect of the 
matter in detail, but it is important at the outset to grasp the 
conception that the final end and aim of metabolism is to sup- 
ply energy for the vital activities and that the demand for en- 
ergy is the controlling factor in all its processes. It is these 
transformations of energy which, if not synonymous with life, 
are at least its objective manifestation. 

But while it is essential to hold fast to this broad general con- 
ception of metabolism, it is also important to understand clearly 
that the processes by which this end is reached are exceedingly 
complex. A volume would be required for any adequate dis- 
cussion even of existing knowledge regarding the details of the 
metabolic processes. Such a discussion lies outside the scope 
of the present work. All that is attempted in this chapter is 
to outline the metabolism of the principal groups of feed sub- 
stances and, as preliminary to a subsequent consideration of 
their values as sources of matter and energy to the body, to 
indicate the functions which they perform in the building up 
and maintenance of the organism and the support of its activ- 
ities. 

§ 2. Enzyms as Agents in Metabolism 

Enzym action has come to play so large a part, even if a more 
or less hypothetical one, in the current conceptions of the pro- 
cesses of metabolism that a brief outline of the prevailing 
views seems called for. 

208. Extracellular enzyms. — The enzyms of the digestive 
tract are those which are most familiar in physiology. As has 
been seen (114), the digestion of all three of the chief classes 



METABOLISM 149 

of feed ingredients is brought about largely or wholly by their 
agency and is often effected by different enzyms in successive 
stages. Thus the ptyalin of the saliva converts starch into 
maltose while the further conversion of the latter into dextrose 
is effected by the maltase of the intestine. Quite similar are 
the successive actions of pepsin, trypsin and erepsin on the pro- 
teins. In all these cases, as well as in the even more familiar case 
of the diastase of germinating seeds, the enzyms act at a dis- 
tance from the cells which produce them and have, therefore, 
been called extracellular enzyms. 

209. Intracellular enzyms. — From the fact that the most 
obvious cases of enzym action were those in which the ferment 
acted at a distance from the cells producing it, enzyms came to 
be regarded as substances whose action belonged in a different 
category from that of living cells. A sharp distinction was 
drawn between unorganized substances, acting substantially 
as chemical reagents, and organisms producing chemical changes 
by virtue of their life. The action of the yeast plant upon sugar 
afforded a typical example of this distinction. It was shown 
that yeast secreted an enzym (invertase) which was capable of 
inverting sucrose independently of the action of the yeast cell,, 
while, on the other hand, the alcoholic fermentation of mono- 
saccharids was held to be a vital function of the living yeast 
cells. 

Buchner, however, in 1897, showed that by suitable means 
there could be extracted from yeast a substance (zymase) 
which fermented the simple sugars exactly like yeast in the 
absence of any living organism whatever; i.e., it acted as an 
enzym. It became evident, then, that the yeast cell ferments 
monosaccharids not because it is alive but because it contains 
zymase. The only essential difference between the yeast fer- 
mentation and that, for example, produced by diastase or by 
the invertase of yeast is that the enzym normally acts within 
the cell which produces it. Later it was shown that what is 
true of the yeast fermentation is true also of the fermentation 
caused by the lactic acid bacillus. It, too, is due to an intra- 
cellular enzym which can be separated from the cell and act 
independently. Investigators are inclined, therefore, to re- 
gard all fermentation as the work of enzyms, some of which, 
like the digestive enzyms, are excreted by the cells and may 



150 NUTRITION OF FARM ANIMALS 

act at a considerable distance from their point of origin, 
while others normally produce their effect within the secret- 
ing cell. 

210. Intracellular enzyms in the body. — Still more recently 
the presence of intracellular enzyms in all parts of the animal 
body has been recognized. It has been shown that a very 
considerable variety of reactions which are known to take place 
in the body may also be brought about outside the body by the 
action of extracts of various tissues and organs under conditions 
apparently excluding the action of any living organisms. Con- 
sequently, they have been ascribed to the action of enzyms 
originally present in the cells, and the reactions in the body 
have been regarded as due to these same enzyms. The 
idea of intracellular enzyms has thus been extended to account 
for the metabolic activities of the organism, and this explana- 
tion has been very generally accepted by physiologists. Accord- 
ing to this view, the body cells bring about metabolic changes 
substantially in the same way as do the cells of yeast or of 
the lactic acid bacillus, viz., by the formation of appropriate 
enzyms which act upon the substances to be metabolized. 
This phase of the subject is a comparatively new one 
and unanimity as to individual cases has by no means been 
reached, but of the value of the general conception as a working 
hypothesis there can be little question. 

The word explanation is used above, of course, in a limited 
sense. It is not known how the cell produces enzyms, nor with 
any degree of certainty how an enzym acts. Nevertheless, 
this hypothesis, if confirmed, is a real explanation as far as it 
goes, in that it enables related phenomena to be grouped to- 
gether from a broader standpoint, as will be apparent from the 
following paragraphs. 

211. Enzym reactions reversible. — A chemical reaction is 
said to be reversible when it may progress in either direction 
according to the conditions. For example, if a mixture of hydro- 
gen and iodin in molecular proportions be heated to 448°C. 
hydrogen iodid is produced. If, however, hydrogen iodid be 
heated to the same temperature it yields hydrogen and iodin. 
The reaction between these two elements, then, is represented 
by the equation 

H 2 + I 2 ^ (HI) 2 



METABOLISM 151 

At the temperature of 448 C, 79 per cent of the matter exists 
as HI and the remainder as free H 2 and I 2 ; the HI is dissoci- 
ated at the same rate at which the H 2 and I 2 unite, and a con- 
dition of chemical equilibrium exists. At a different temper- 
ature, the point of equilibrium is different, but otherwise the 
result is the same. In theory, all chemical reactions are regarded 
as reversible, but in many cases the reverse action is so slight as 
to be incapable of detection under attainable experimental 
conditions, and such reactions are often spoken of as irreversible. 

In addition to the temperature, the position of the point of 
equilibrium in a reversible reaction is affected by the relative 
mass of the ingredients. Thus if, in the example just given, 
the iodin be removed from the field of chemical action (as, for 
example, by condensing it to the solid form in a cold portion 
of the apparatus) the dissociation of the hydrogen iodid will 
proceed until it is practically complete. On the other hand, 
if the hydrogen iodid be removed (as by allowing it to react 
with calcium carbonate) the reaction may be pushed to 
completion in the reverse direction. Similarly, an increase in 
the concentration of one of the reacting substances tends to dis- 
place the equilibrium in the opposite direction. 

It is a matter of much interest that at least some enzym 
reactions have been shown to be reversible. One of the best 
authenticated cases appears to be that of the action of lipase on 
fats. It has been shown by Kastle and Loevenhart x that this 
enzym acts on ethyl butyrate according to the equation 

C2H5 • C 4 H 7 2 + H 2 ^ C 2 H 5 OH + C 4 H 8 2 

A similar reaction has also been shown to take place with 
monobutyrin, the glycerol ester of butyric acid, which may be 
regarded as a simple fat, while it is at least very probable that 
the higher fats are acted on in the same way. Another example 
of reversible enzym reaction is claimed to be that of the con- 
version of maltose into dextrose by the action of the ferment 
maltase, it appearing, according to the researches of Croft 
Hill, 2 that the same ferment may also convert dextrose into 
maltose. Similar, although less decisive, results have also been 
reported regarding the action of the proteases. 

1 Amer. Chem. Jour., 24 (1900), 491. 

2 Jour. Chem. Soc, Trans., 73 (1898), 634. 



152 NUTRITION OF FARM ANIMALS 

212. Reversibility of metabolic reactions. — It would appear, 
then, that the action of the intracellular enzyms which are be- 
lieved to play such an important part in metabolism may be 
synthetic as well as analytic, and that the metabolic processes 
may be conceived of as a complex of reversible chemical reac- 
tions, now accelerated and now retarded by appropriate en- 
zyms. 1 The idea that each cell of the body thus exists in a 
state of constantly shifting chemical equilibrium, according as 
the concentration of one or another substance in its domain 
changes, is an attractive one in its breadth and comparative 
simplicity, and there seems to be little doubt that it contains 
elements of truth and will prove an important aid to research. 
As yet, however, it is to be regarded as a probable hypothesis 
rather than as a fully established fact. 

§ 3. The Metabolism of the Carbohydrates 

The hexose carbohydrates 

213. Glycogenic function of the liver. — The monosac- 
charids (principally dextrose) produced in the digestive cleavage 
of the carbohydrates are resorbed chiefly or wholly by the blood 
capillaries of the intestines. These capillaries unite into the 
portal vein leading to the liver, where it subdivides into a 
capillary system in which the blood is brought into intimate 
contact with the cells of that organ and from whence it passes 
by way of the hepatic vein into the posterior vena cava, thus 
entering the general circulation (182). 

The proportion of dextrose found in the blood of the general 
circulation is remarkably constant, and if any considerable 
excess be introduced it is promptly excreted through the kid- 
neys (198). On the other hand, the supply of carbohydrates 
from the digestive tract may be more or less intermittent or 
fluctuating, so that there is evidently need for some regula- 
tory mechanism to prevent a waste of sugar by excretion in 
the urine. This regulation is effected chiefly in two localities, 
viz., in the muscles and in the liver. The function of the liver 

1 That syntheses can be eSected by the agency of enzyms seems established, but 
that enzym reactions in general are reversible is questioned by good authorities. 
For example, the ferment maltase, acting on dextrose, is stated to produce not mal- 
tose but isomaltose, and it is claimed that a different enzym is required to reconvert 
isomaltose into dextrose. 



METABOLISM 1 53 

in this respect was the earliest to be discovered and may be 
appropriately considered first. 

When dextrose is being freely resorbed from the digestive 
tract, it undergoes dehydration and polymerization in the liver, 
yielding the polysaccharid glycogen (25), which is stored up 
in the liver cells. If, on the other hand, the resorption of dex- 
trose from the intestines is insufficient to maintain the supply 
in the blood, glycogen previously formed may undergo the 
reverse process of hydration and cleavage, giving rise to a pro- 
duction of dextrose. This regulatory activity, discovered by 
Claude Bernard in 1853, by which carbohydrates are held back 
or released according to the demands of the body, is called the 
glycogenic function of the liver. While this function has other 
aspects, as will appear later, as respects the digested carbohy- 
drates the liver may be likened to a storage reservoir by which 
the flow of a stream is controlled. 

214. Mechanism of regulation. — It is of interest to note 
that this phase of carbohydrate metabolism illustrates two of 
the general conceptions formulated on preceding pages. 

First, the formation of glycogen is a synthetic reaction. The 
comparatively simple molecules of dextrose are built up tem- 
porarily into the more complex molecules of the polysaccharid. 
In other words, almost the first step in carbohydrate metabolism 
is an anabolic change (203). 

Second, the process of the formation and destruction of gly- 
cogen is susceptible of explanation as a reversible enzym re- 
action (212). It is known that the conversion of glycogen into 
dextrose is effected by an enzym or enzyms which may be ex- 
tracted from the liver and which, it would seem, must be similar 
to those of the digestive tract. The action of one of the latter, 
maltase, however, is claimed to be reversible (211), and one is 
naturally tempted to infer that the synthesis of the liver gly- 
cogen is effected by the same enzym which brings about its cleav- 
age, although experimental proof that such is the case is lacking. 
According to this hypothesis, the changes taking place in the 
liver would be represented by the equation 

n (C 6 Hi 2 06) ^_ C 6 nHi0nO5n + n(H 2 0) 

An excess of dextrose in the blood would have the effect of 
displacing the point of equilibrium in the direction of the for- 



154 NUTRITION OF FARM ANIMALS 

mation of glycogen, while a deficiency of dextrose would have the 
contrary effect. If it be supposed further that the glycogen 
as soon as formed combines with the protoplasm of the liver 
cells, forming compounds which withdraw a considerable por- 
tion of it from the sphere of action of the enzym, after the anal- 
ogy of the precipitation of an insoluble compound, we have a 
plausible, even if chiefly hypothetical, scheme of the chemical 
mechanism of the process. Whether or not it adequately rep- 
resents the actual facts, it may at least serve as a concrete il- 
lustration of the manner in which the conception of enzym ac- 
tion may be applied to metabolic processes. 

215. Muscle glycogen. — While the glycogenic function of 
the liver has been the subject of very extensive investigation, 
the presence of glycogen is by no means confined to this organ. 
Indeed, glycogen seems to be a normal constituent of animal 
protoplasm. It is found in greater or less amounts in practi- 
cally all tissues, being particularly abundant where rapid cell 
multiplication is taking place, as in embryonic tissues or in 
rapidly growing tumors. It is estimated that in an animal in 
normal condition roughly one-half of the glycogen of the body 
is contained in the liver. Of the other half by far the larger 
proportion is found in the muscles (96). 

The glycogen of the muscles (and other organs) is not simply 
glycogen which has been formed in the liver and transported to 
the muscles, but is produced independently from the dextrose 
of the blood, apparently in much the same manner as in the 
liver. That this is true is shown by the fact that glycogen is 
still formed in the muscles when, by surgical interference 
(Eck fistula), the blood is prevented from passing through the 
liver. In fact, the formation of glycogen in the muscles, etc., 
appears to be the primary process, while the liver serves rather 
as a secondary reservoir which may be eliminated without 
seriously affecting the general carbohydrate metabolism. With 
the liver excluded from the circulation, the dextrose resorbed 
from the digestive tract is still converted into glycogen and the 
animal is still able to digest considerable quantities of carbohy- 
drates without the appearance of sugar in the urine. 

Even in the normal animal, however, the power to dispose of sur- 
plus sugar is not unlimited. If large quantities of sugar are consumed, 
the conversion into glycogen, together with the normal katabolism, 



METABOLISM 1 55 

may not keep pace with the resorption and there occurs an excretion 
of sugar in the urine — the so-called " alimentary glycosuria." The 
amount of sugar which can be resorbed without producing alimentary 
glycosuria, — i.e., the limit of tolerance for sugar — varies with the 
kind of sugar, being highest with dextrose (220) . 

216. Carbohydrates formed in the body. — In their relation 
to the carbohydrates of the feed, the muscles and liver act, as 
has been seen, as a sort of storage reservoir or regulator of the 
sugar supply to the blood. The total withdrawal of carbohy- 
drates from the feed, however, by no means results in the 
disappearance of these substances from the body. The car- 
bohydrates appear to be essential to the normal course of metab- 
olism and if they are absent from the feed, they are manufac- 
tured in the body from other materials. A carnivorous animal, 
e.g., fed exclusively on meat or fat, shows a normal percentage 
of dextrose in its blood, while its liver and muscles contain a 
normal amount of glycogen. It is true that in such an experi- 
ment small quantities of glycogen are contained in the meat 
consumed, but their amount is entirely insignificant as com- 
pared with the quantities of dextrose which there is reason to 
believe are produced and katabolized in the organism. This 
dextrose must obviously have its origin either in the proteins or 
the fats. Which of the two is the source or whether both can 
be thus utilized will be considered later in connection with 
the metabolism of those substances (235, 253). 

217. Formation of fat. — The mutual transformations of 
sugar and glycogen tend to keep the dextrose content of the 
blood approximately constant, while holding a supply of readily 
available carbohydrate material at hand to meet promptly any 
sudden demand. The amount of carbohydrates which can be 
disposed of in this way is, however, limited. For man it is 
estimated at about 300 grams and for cattle at about 2 kilo- 
grams (96). It is evident, then, that if the feed contains a per- 
manent excess of carbohydrates over the needs of the body the 
capacity to store them up as glycogen will soon be exhausted. 
A surplus of carbohydrates over the amount which can be dis- 
posed of in this way is applied by the organism to the pro- 
duction of fat, which may be stored up in very large amounts 
in the cells of connective tissue through the body, but especially 
in those immediately beneath the skin and about the abdominal 



156 NUTRITION OF FARM ANIMALS 

organs, constituting the adipose tissue (94). This tissue con- 
stitutes a reserve of non-nitrogenous material which may be 
mobilized later if need arises. 

Of the chemistry of the conversion of carbohydrates into 
fats, as well as of the organ or organs where it is effected, 
our knowledge is still meager, but the fact of such a change 
is undisputed and it is perhaps the most notable example 
of a synthetic and anabolic process in the animal body. 
The physiological evidence for this fact and the quantitative 
relations of the process may be taken up more conveniently 
later (249). 

218. Katabolism of carbohydrates. — The physiological sig- 
nificance of the dextrose of the blood and the glycogen of the 
muscles and liver appears most clearly when they are regarded, 
not in the light of a more or less temporary storage of matter 
in the body, but rather as carriers of energy for the physiological 
processes. Of these processes, the most obvious one, which 
vastly predominates over all others, is the performance of work 
by the muscles, external and internal, but what is true of mus- 
cular work is in the main true also of the subordinate forms of 
glandular and cellular activity. The former, therefore, may 
be taken as typical. 

In the performance of muscular work, as will appear later, 
there is a rapid katabolism of non-nitrogenous material and 
especially of carbohydrates, largely, it would appear, in the form 
of dextrose. The resulting impoverishment of the blood in 
dextrose causes a conversion of stored up glycogen into dextrose 
to supply the lack. If the view of the formation of glycogen 
which regards it as a reversible reaction may be accepted, we 
may say that the chemical equilibrium between the dextrose 
and the glycogen is disturbed by the removal of the former 
during muscular work. As long as the work is continued, the 
process of conversion of glycogen into dextrose also continues, 
and by prolonged work it is possible to reduce the glycogen con- 
tent of an animal to a very low limit. 

It should be clearly understood that the foregoing is only a 
highly schematic view of the chemistry of muscular contraction 
as related to the katabolism of the carbohydrates. Some further 
consideration is given in Chapter XIV (630) to the very com- 
plicated chemical mechanism of the process. 



METABOLISM 



57 



219. Intermediary katabolism. — Regarding the intermediary 
katabolism of the carbohydrates, not very much is known. 
It appears probable, however, that dextrose undergoes pre- 
liminary cleavage with the formation of glyceric aldehyde, 
pyruvic aldehyde (methyl glyoxal) and either lactic or pyruvic 
acid, which is then further oxidized to acetic acid, carbon dioxid 
and water. Many facts, including especially those derived 
from a study of the fermentation of sugar, seem to point to the 
possibility of such reactions. Lactic acid is also widely dis- 
tributed in the body, although its presence is also susceptible 
of explanation as arising in the katabolism of protein (233), 
and, moreover, it has been shown that lactic acid may give rise 
to glycogen or dextrose in the animal body. Accordingly, 
these changes, like the mutual transformations of glycogen and 
dextrose, may be conceived of as constituting a series of re- 
versible reactions. 

(Dextrose) 

Glycogen ^ CH 2 OH(CHOH) 4 CHO 

(Glyceric aldehyde) 

CH 2 OH(CHOH) 4 CHO ^t 2CH 2 OH • CHOH • CHO 

(Pyruvic aldehyde) 

CH 2 OH • CHOH • CHO-H 2 ^ CH 3 • CO • CHO 

(Lactic acid) 

CH 3 • CO • CHO + H 2 ^ CH3CHOH • COOH 

or 

(Pyruvic acid) 

CH • CO • CHO • + O ^ CH3CO • COOH 

The conversion of dextrose into lactic acid is a nearly iso- 
thermic process, the resulting lactic acid containing almost the 
same amount of chemical energy as the dextrose. If, then, 
these cleavages occur in the katabolism of carbohydrates they are 
obviously preparatory to the actual oxidation in which the 
principal portion of the energy is liberated. 

The pentose carbohydrates 

. The foregoing paragraphs have treated of the metabolism of 
the hexoses, which constitute the chief carbohydrate supply of 
man, and of the carnivora so far as the latter consume carbo- 
hydrates. The feed of herbivora, however, contains also consid- 
erable amounts of various pentose carbohydrates which are in part 



158 NUTRITION OF FARM ANIMALS 

digestible, or at least disappear from the feed during its passage 
through the alimentary canal. 

220. Pentose sugars. — In general, it may be stated that the 
pentose sugars (in particular arabinose and xylose), whether 
administered by the stomach or injected into the blood, are at 
least partially oxidized in the body. The pentoses differ from 
the hexoses chiefly in the fact that the limit of tolerance in the 
blood (215) is lower. Excessive amounts of hexose carbohy- 
drates cause an excretion of sugar in the urine. The same 
effect is produced by the pentoses, but much smaller quantities, 
relatively, are required to bring it about. 

Most, although not all, investigators have found an increase 
in the glycogen of the liver consequent upon the ingestion of 
pentoses, but in every case it has been the ordinary C6 glycogen, 
indicating that the effect is an indirect one. 

221. Pentosans. — The investigations upon the soluble 
pentose sugars or their derivatives just referred to have shown 
that they are to a greater or less extent assimilable. The pen- 
tose carbohydrates in the feed of herbivora, however, exist to a 
very limited extent, if at all, in this form. They are chiefly 
polysaccharids, being either pure pentosans or combinations 
of pentosans and hexosans. In discussing the nutritive value 
of these pentosans, it seems to have been frequently assumed that 
they are converted into pentoses during digestion. As a matter 
of fact, however, there is no direct evidence that such is the case, 
while Kellner's results (129) afford reason to believe that they 
are largely fermented along with cellulose, yielding, besides 
gaseous products, chiefly organic acids. If this is the case, 
farm animals do not acquire from their feed any considerable 
amounts of pentoses and conclusions drawn from experiments 
with the pentose sugars regarding the nutritive value of these 
substances are inapplicable to ordinary stock feeds. Their 
true value in the latter would be simply that of the products of 
their fermentation. 

The organic acids 

222. Formation in digestion. — As was shown in Chapter 
IV (128-130, 132), a considerable proportion of both the hexose 
and pentose carbohydrates contained in the feed of herbivora 
undergoes fermentation in the digestive tract, giving rise, in 



METABOLISM 159 

addition to gaseous products, to the formation of various or- 
ganic acids. In particular, the constituents of the cell walls 
of plants appear to owe their apparent digestibility chiefly to 
this action of the organized ferments of the alimentary canal. 
While, therefore, the organic acids are chemically distinct from 
the carbohydrates, and while some of these acids are contained 
as such in the feed, the amounts produced from carbohydrates 
are so considerable that this would appear an appropriate 
point at which to consider their metabolism. 

Unfortunately, however, little is known of the metabolism of 
the simpler organic acids, beyond the fact that such of them 
as have been subjected to experiment are katabolized to carbon 
dioxid and water, not more than traces of them at most ap- 
pearing in the excreta. A portion of the carbon dioxid pro- 
duced unites with alkalies and appears in the urine as carbonates. 

223. Analogy with carbohydrates. — It is interesting to re- 
call in this connection that the carbohydrates themselves 
undergo cleavage, producing lactic or even acetic and formic 
acids, before their final oxidation (219). If it be true that these 
latter comparatively simple substances are those whose oxida- 
tion yields most of the energy supplied by the carbohydrates, 
there would seem to be no reason why the same acids resorbed 
directly from the digestive tract should not follow the same 
general course of metabolism and have substantially the same 
nutritive value. If this view be correct, there is after all a con- 
siderable similarity between the metabolism of the carbohy- 
drates and that of their fermentation products. 

The non-nitrogenous matter of the urine 

224. Products of incomplete katabolism. — It has been im- 
plied in the foregoing pages that the digested carbohydrates of 
the feed, whatever the intermediate stages through which they 
may pass, are ultimately oxidized to carbon dioxid and water. 
Of the ordinary hexose carbohydrates this is doubtless true, but 
with some of the large variety of substances ordinarily grouped 
together in the conventional scheme of feeding stuffs analysis 
as " carbohydrates and related bodies," or as " crude fiber " 
and " nitrogen-free extract," the case appears to be otherwise. 

It has been shown that the urine, in addition to the nitrogenous 



160 NUTRITION OF FARM ANIMALS 

products of protein katabolism which will be considered in the 
following section, contains also non-nitrogenous materials, 
presumably arising from the incomplete katabolism of ingredi- 
ents of the feed. In the urine of man and of the carnivora these 
non-nitrogenous substances are chiefly or wholly such as might 
be derived from the katabolism of proteins (phenols and other 
compounds of the aromatic series), and their amount is com- 
paratively small. In the urine of herbivora, particularly of 
ruminants, however, their quantity is relatively very consid- 
erable, and it seems impossible to regard any large portion of 
them as products of protein katabolism. 

225. Origin. — Apparently these non-nitrogenous organic 
substances originate in some way from the roughages. Their 
proportion in the urine is relatively large when the ration con- 
sists exclusively of roughage, and the addition of such feeding 
stuffs to a basal ration causes a marked increase in their amount, 
while, on the other hand, such concentrates as have been in- 
vestigated do not produce this effect to any very considerable 
extent. Furthermore, their amount seems to bear no fixed 
relation to the protein of the feed. When the amount of the 
latter ingredient is small, the total organic matter of the urine 
has in some cases exceeded the digested protein of the feed, thus 
demonstrating that a portion at least of the non-nitrogenous 
urinary constituents must have had some other source. As 
the proportion of protein in the feed increases, the amount of 
nitrogenous products in the urine likewise increases, while that 
of the non-nitrogenous products appears to be more constant, 
so that the ratio of urinary nitrogen to carbon increases. The 
most plausible explanation of these facts seems to be that the 
substances in question are derived from some of the non-nitroge- 
nous ingredients of the roughages, but from what ones, or 
what is the nature of the products, we are still ignorant. 

§ 4. The Metabolism of the Simple Proteins 

Anabolism 

226. Synthesis of proteins from digestive products. — The 
simple proteins are resorbed (139, 152) in the form of com- 
paratively simple cleavage products; largely as amino acids 
but in part perhaps as more or less complex polypeptids. Out 



METABOLISM 161 

of these substances the body builds up the great variety of 
specific proteins which are peculiar to itself and which differ in 
properties and chemical structure from the proteins of the feed, 
especially from those of the vegetable kingdom (147). This 
process of building animal proteins from the fragments of 
vegetable proteins is the most conspicuous example at once of 
the synthetic powers of the animal organism and of the object 
of the digestive cleavage. 

227. Seat of protein synthesis. — As regards the place where 
this synthesis of proteins occurs, opinions are divided. Until 
recently, most experimenters have not been able to detect the 
products of digestive cleavage with certainty in the blood, either 
in the general circulation or in the portal vein, and the current 
view has been, therefore, that of Abderhalden, viz., that the 
" building stones " of the proteins are synthesized in the 
epithelial cells of the intestine and that the resulting proteins 
— in particular serum albumin — are passed on to the blood 
to serve as nourishment to the protein tissues of the body. 

Various investigators, however, have reported the presence in 
the blood of greater or less amounts of non-protein nitrogen 
and with the aid of more refined chemical methods Folin and 
Denis 1 and Van Slyke and Meyer 2 seem to have shown beyond 
question that amino acids may pass through the resorbing 
epithelium unchanged and be found in the blood and tissues 
in amounts sufficient to account for practically all that was 
administered (152). The latter experimenters have likewise 
shown that after meat feeding the proportion of amino acids in 
the blood may be doubled and that the increase affects the blood 
of the entire circulatory system and not that of the portal vein 
only, while Abel, 3 by a diffusion method, has been able to 
secure considerable amounts of amino acids from the circulat- 
ing blood of living animals. The evidence at the present time, 
therefore, seems decisively in favor of the view that the frag- 
ments into which the protein molecule is split during digestion 
pass without material change into the blood current and serve 
as a common source from which the proteins, both of the blood 
and the various tissues, are built up and that every living cell, 
each in its own measure, has this anabolic power. 

1 Jour. Biol. Chem., 11 (1912), 87. 2 Jour. Biol. Chem., 12 (1912), 399. 

3 Jour. Pharmacol, and Expt'l Therap., 5 (1914), 275. 
M 



1 62 NUTRITION OF FARM ANIMALS 

Katabolism 

228. Nitrogenous end products. — The total katabolism of 
the proteins results in the elimination of all their nitrogen 
through the kidneys in the form of the various relatively simple 
crystalline products found in the urine. Of the nitrogenous 
excretory products of man and the carnivora, urea is the most 
prominent, while others, such as uric acid, creatin, creatinin, 
ammonia, etc., are of subordinate importance quantitatively. 
Traces of hippuric acid are also found in the urine of man and 
carnivora, while it is present in relatively large amounts in that 
of herbivora along with considerable quantities of ammonia 
and apparently but little urea. 

The nitrogenous ingredients of the urine of mammals other 
than those just mentioned are either derived chiefly from the 
nucleoproteins, whose metabolism will be considered later, 
or are present in such small amounts as to call for no special 
consideration from the present very general point of view. 
Finally, it should be noted for completeness that a small amount 
of nitrogenous products is eliminated in the perspiration and 
also that from one point of view the incompletely katabolized 
nitrogenous excretory products of the feces (154) may also be 
regarded as products of protein katabolism. 

Urea, or dicarbamid, CO (NH 2 )2, is the chief nitrogenous product 
of the katabolism of the simple proteins in carnivora and omnivora. 
In human urine from 8o to 90 per cent of the nitrogen is ordinarily 
present in this form, although the proportion may be considerably 
diminished under special conditions, notably on a low protein diet. 
Urea, however, is not simply split off as such from the proteins as 
some earlier schematic statements have sometimes been taken to 
imply. The immediate antecedent of urea is ammonium carbonate, 
which undergoes a dehydration in the liver or elsewhere, while there 
is evidence in favor of the view that the ammonia is brought to the 
liver in the form of ammonium lactate. At any rate it is an accepted 
fact that most, if not all, of the nitrogen of the simple proteins passes 
through the ammonia stage on its way to excretion as urea. 1 That 
the formation of urea from ammonia is not exclusively a function of 
the liver is shown by the fact that it still continues when this organ 
is excluded from the circulation by means of an Eck fistula. 

1 It has been, shown that the liver, kidneys and other organs contain an enzym 
which splits off the guanidin group from arginin (47) producing urea and ornithin. 



METABOLISM 



163 



Hippuric acid in small amounts is a normal constituent of the 
urine of mammals but is especially abundant in that of herbivora. 
Its formation is the result of a synthesis (204). When benzoic acid 
or other compounds containing the benzoyl radicle are introduced 
into the circulation they are paired with glycin, one of the cleavage 
products of the proteins, in the kidneys and excreted as hippuric 
acid, which, chemically, is benzoyl-glycin, or benzamidoacetic acid, 
(C6H5 • CO)NHCH 2 • COOH. The normal presence of small quan- 
tities of hippuric acid in the urine arises from the fact that the putre- 
faction of the proteins in the intestines yields compounds containing 
the benzoyl radicle which are resorbed and combine with glycin to 
form hippuric acid. But a small proportion of the hippuric acid pro- 
duced by herbivora can be thus accounted for ; however. Most of it 
appears to owe its origin to the roughages consumed by these animals, 
especially those derived from plants of the gramineae, while, on the 
other hand, concentrates do not seem to increase its amount. Ap- 
parently its formation bears some relation to some of the ingredients 
of the cell walls, but to what ones in particular is not clear. 

229. The non-nitrogenous residue. — In addition to the 
nitrogenous products eliminated in the urine, the complete 
oxidation of the protein molecule gives rise to the production 
of considerable amounts of carbon dioxid and water, which are 
excreted through the same channels as those derived from the 
katabolism of carbohydrates or fats. To put the matter in the 
reverse way, while the urinary products account for all the 
nitrogen of the protein, they contain but a relatively small 
part of its carbon, hydrogen and oxygen. This is clearly shown 
by comparing the average amounts of these elements in 100 
parts of protein w T ith the quantities contained in the urea 
corresponding to the total nitrogen of the protein. Disregard- 
ing the sulphur of the proteins, the results of such a computation 
are as follows : — 



Carbon . 
Hydrogen 
Oxygen . 
Nitrogen 



Proteins 



53-o 
7.0 

24.0 
26.0 

100. o 



Urea 



6.86 

2.29 

9.14 

16.00 

34-29 



Residue 



46.16 

4.71 

14.86 

65-7I 



1 64 NUTRITION OF FARM ANIMALS 

After abstracting the elements of urea, there remains con- 
siderably over half the hydrogen and oxygen of the protein and 
the larger part of its carbon. A substantially similar result is 
reached in case of the other nitrogenous metabolic products. 
The splitting off of these products from the proteins leaves a 
non-nitrogenous residue. 

230. Two stages of protein katabolism. — Two general stages 
in the katabolism of the proteins may be distinguished. The 
first is a hydrolysis by which the proteins are split up into their 
constituent amino acids. The second is a deaminization of 
the amino acids in which the nitrogen of these acids is split off 
as ammonia. 

231. Protein hydrolysis. — The first stage in the katabolism 
of the body proteins is a hydrolytic cleavage, more or less 
similar to that effected in digestion and like the latter brought 
about by enzyms, which in this case are contained in the body 
cells — the intracellular enzyms (209). 

The truth of this view is attested by the facts that the pres- 
ence of proteases in almost all of the tissues and organs of the 
body has been demonstrated and that under proper conditions 
they effect a rapid solution of the tissue proteins — the so-called 
autolysis. Further confirmation is afforded by the known 
facts regarding the transformation of one protein into another 
in the body, while finally the production in the organism of 
some of the cleavage products of the proteins, presumably as 
products of katabolism, may be indirectly shown. 

232. Is protein hydrolysis a reversible process ? — If the 
katabolism of body proteins is initiated by an enzymatic cleav- 
age in the body cells, this is precisely the reverse of the syn- 
thetic action by which it is believed that body proteins are 
built up out of the products of digestive cleavage (226), and 
the question at once arises whether we have to do here with a 
reversible enzym reaction, analogous to that which has been 
suggested as occurring in the case of the carbohydrates (214), 
the general nature of which may be represented by the formula 

Protein ^ Amino acids 

It must be freely admitted that proof of the reversibility of 
the action of proteolytic enzyms is as yet lacking, such phenom- 
ena as the formation of the plasteins discovered by Okunew 



METABOLISM 165 

and the alleged formation of paraneuclein by the action of pep- 
sin as reported by Robertson being apparently due to adsorp- 
tion phenomena. 1 On the other hand, however, many authori- 
ties 2 are inclined to regard reversibility as a general charac- 
teristic of enzym action and mere negative evidence cannot, of 
course, disprove this belief. At any rate the conception of 
a reversible reaction between the amino acids of the blood and 
lymph and the proteins of the cells affords a comparatively 
simple and unforced explanation of the facts outlined in the 
foregoing paragraphs, as well as of others relating to the in- 
fluence of the supply of feed protein on metabolism which will 
be considered later (402). In particular, it may be observed 
that, according to this view, by no means all the amino acids 
resorbed. into the blood stream would undergo synthesis to 
proteins but that, especially if the amino acid supply were 
liberal, a large part of them might pass directly to the second 
stage of protein katabolism, viz., deaminization. 

Finally, since the proportions of the single amino acids sup- 
plied from the digestive tract vary, one must conceive, not of 
a single reaction between protein and amino acid, but, speak- 
ing broadly, of as many independent reversible reactions as 
there are amino acids concerned. 

233. Deaminization. — The second general stage of protein 
katabolism seems to be the splitting off of the NH 2 group from 
the amino acids, the products being the corresponding or closely 
related non-nitrogenous organic acids on the one hand and 
ammonia on the other. This also, it would appear, is a case 
of enzym action, although the discovery of deaminizing enzyms 
in various tissues is comparatively recent and its biological im- 
portance is still to some extent speculative. 

The ammonia resulting from the deaminization of the amino 
acids is believed to be the immediate antecedent of urea, into 
which it is rapidly converted, chiefly although not exclusively 
in the liver (228). In this way the nitrogen of any amino acids 
resorbed in excess of the immediate demands of the body cells 
for protein building material is promptly converted into ex- 
cretory products and so disposed of, while the larger part of 
their carbon and hydrogen remains in a series of substances 

1 Compare Rohonyi ; Biochem. Ztschr., 53 (1913), 179. 

2 Compare Bayliss; The Nature of Enzym Action (1908), Chapter V. 



1 66 NUTRITION OF FARM ANIMALS 

bearing a more or less close relation to the fatty acids and to- 
gether constituting the " non-nitrogenous residue " of the 
proteins (229). 

It is important to note that these non-nitrogenous products 
contain the larger share of the chemical energy of the original 
proteins, the ammonia carrying off but little and both the di- 
gestive cleavage and the deaminization being nearly isothermic 
processes. The cleavage and deaminization of proteins, there- 
fore, do not necessarily involve a destruction of their nutritive 
value and the excretion of a given amount of nitrogen in the 
urine is not to be regarded as indicating the total destruction 
of a corresponding amount of protein. It has ceased to exist as 
protein, but its non-nitrogenous residue is made up of substances 
which are closely related chemically to both the carbohydrates 
and fats, and which, like these, may be katabolized to supply 
energy. 

234. Deaminization reversible. — Since deaminization in the 
body appears to be an enzymatic reaction, it is natural to in- 
quire whether in this case, as in the other enzymatic reactions 
already considered, there is any evidence that the reaction is 
a reversible one. 

So far as direct experiments with deaminizing enzyms are 
concerned, no such evidence has been produced, but Knoop l 
andEmbden and Schmitz 2 have demonstrated a fact of funda- 
mental significance in metabolism, viz., that amino acids may 
be formed in the body from ketonic or hydroxy acids and am- 
monium salts. In other words, the animal body can manufac- 
ture some at least of the " building stones " of the proteins, 
and from the latter presumably the proteins themselves (226), 
out of the ammonium salts of the corresponding ketonic or 
hydroxy acids. The full significance of this comparatively 
recent discovery is not yet fully apparent. The question of the 
utilization of ammonium salts will be considered later. In 
this connection the important fact is that these results indicate 
that the reaction, or series of reactions, by which deaminization 
takes place is reversible, so that the whole process of protein 
metabolism may be represented schematically as follows : — 

_.._... • j _> [ Organic acids 

Proteins ^ Ammo acids Zt. \ A 

^ { Ammonia 

1 Ztschr. Physiol. Chem., 67 (1910), 489. 2 Biochem. Ztschr., 29 (1910), 423. 



METABOLISM 1 67 

235. Formation of carbohydrates from proteins. — It has 

already been stated (216) that carbohydrates may be manu- 
factured, in the bodies of carnivorous animals at least and 
probably in those of other species, but the question whether 
the proteins or the fats or both serve as the source was left 
open. 

Without entering into experimental details, it may be stated, 
as the general result of many trials in which the possibility 
of a production from fats was excluded as completely as pos- 
sible, that carbohydrates have been produced in such large 
amounts, and in quantities so closely paralleling the quantities 
of protein katabolized, as to amount to a proof of their formation 
from the latter. The acceptance, however, of the view that 
carbohydrates may be a product of protein katabolism by no 
means excludes the possibility of their formation also from fats. 
Indeed, in view of the importance of carbohydrates in metab- 
olism it seems altogether likely that the body has the power 
to manufacture them from both fats and proteins, while, as 
already stated (217), the reverse process of the formation of 
fats from carbohydrates has been demonstrated. 

With the increasing knowledge of the details of protein 
katabolism afforded by recent investigations, the question 
under consideration has assumed a somewhat different aspect, 
the discussion shifting from the fate of the proteins as a whole 
to that of the single amino acids and of the non-nitrogenous 
products of their katabolism. It has been shown, especially 
by the work of Lusk and his associates, that some at least of the 
amino acids (glycin, alanin, aspartic acid, glutamic acid, histi- 
din), after deaminization may yield dextrose. In the case of 
glycin and alanin all the carbon of the amino acid could be re- 
covered in the form of dextrose. In the case of aspartic and 
glutamic acids, on the other hand, only three out of the four or 
five carbon atoms respectively were found in the dextrose pro- 
duced. Still other amino acids, notably leucin and tyrosin, 
apparently do not yield dextrose, but instead compounds like 
/3 hydroxybutyric acid and aceto-acetic acid which are the 
distinctive products of the katabolism of the higher fatty acids 
(252). 

In the case of some, then, but apparently not all, of the prod- 
ucts of protein katabolism, the relations between protein and 



1 68 NUTRITION OF FARM ANIMALS 

carbohydrate metabolism may be schematically expressed 
thus : — 



Glycogen $ Dextrose >^\ 
Proteins ^ Amino acids "$■ < 



Lower fatty acids -> CO2 and H 2 



I NH 3 ■» Urea 

236. Formation of fat from proteins. — Since the non-nitrog- 
enous products of protein katabolism appear to consist largely 
of comparatively simple substances closely related to the lower 
members of the fatty acid series, and since some at least of 
these may in all probability be synthesized to carbohydrates, 
while the latter can undoubtedly give rise to fats, it is natural 
to conclude that the non-nitrogenous products of protein 
katabolism may serve as a source of fat, either by direct syn- 
thesis of the simpler fatty acid chains or possibly by way of 
the carbohydrates. The conclusion is one which has been 
hotly debated and much of the earlier evidence in its favor 
has been shown to be inconclusive. The experimental evi- 
dence may be more conveniently considered in connection with 
a discussion of the sources of animal fat (247-249). For the 
present, it may suffice to say that the formation of fat from 
protein seems altogether probable, but that on the other hand 
the amount of fat thus formed under normal conditions is 
usually unimportant. 

§ 5. The Metabolism of the Nucleoproteins 

The metabolism of the conjugated proteins, with the excep- 
tion of the nucleoproteins, offers few features of special in- 
terest. In general it may be said that they are split up into their 
constituents during digestion and that the cleavage products 
undergo substantially the same metabolic changes as if con- 
sumed by the animal in the uncombined form. In the case of 
the nucleoproteins, however, the metabolism of the nucleic 
acid portion of the molecule calls for more specific consider- 
ation. 

Anabolism 

237. Fate of digestive products. — The nucleic acids undergo 
extensive enzymatic cleavages in digestion (139), the products 



METABOLISM 169 

passing into the circulation being essentially phosphoric acid, 
pentoses, and purin and pyrimidin bases. By analogy with 
the simple proteins, one might expect, therefore, to find that 
these fragments of the nucleic acid molecule are rebuilt into 
nucleoproteins in the body cells, of which they constitute such 
an indispensable ingredient (75). 

The occurrence of such a synthesis, however, has been seriously 
questioned. One argument against it is the fact that the in- 
gestion of nucleoproteins, or more specifically purin bases, re- 
sults in a prompt excretion in the urine of end products of their 
katabolism which, although it has not been proved to be quan- 
titative, is certainly large, while the amounts excreted on a 
purin free diet are small and notably uniform. It has been 
argued, therefore, that the so-called " exogenous " purins, i.e., 
the nucleic acid constituents derived from the feed, are simply 
katabolized and excreted without serving to rebuild nucleic 
acids in the cells. Precisely the same argument might be made, 
however, against the synthesis of the simple proteins from their 
cleavage products, since in this case also an increase in the supply 
causes a prompt and almost quantitative increase in the ex- 
cretion of the end product, urea (402). 

238. Autogenesis. — It is true that the formation of nucleo- 
proteins differs from that of the simple proteins in that the 
latter is a reconstruction of the molecule from its fragments l 
rather than a synthesis in the stricter sense, while it has been 
demonstrated that the body can build up nucleic acids out 
of a feed supply containing neither purins, pyrimidins nor 
pentoses. One of the most striking instances of this is 
seen in the development of the embryo of birds and insects. 
The eggs contain practically none of the substances just men- 
tioned, yet the bodies of the young animals contain normal 
amounts of nucleic acid. Equally significant is the case of the 
suckling mammal,which receives in the milk a food very poor 
in purins, pyrimidins and pentoses, yet which maintains a rapid 
growth and cell multiplication with its accompanying formation 
of nucleoproteins. So, too, in Osborne and Mendel's extensive 
investigations 2 upon the nutritive values of the proteins, normal 

1 The possibility of the formation of proteins from ammonia (234) is of little sig- 
nificance under ordinary conditions of nutrition. 

2 Carnegie Institution of Washington, Publication No. 156, p. 85. 



170 NUTRITION OF FARM ANIMALS 

growth of rats through two generations was secured on purin- 
and pyrimidin-free feed. Another fact pointing in the same 
direction is that the body does not appear to require a supply 
of phosphorus in organic combination but can build up its 
organic compounds from phosphates (258). 

239. Regeneration from cleavage products. — In view of 
the capacity of the body to produce nucleoproteins in the 
entire absence of their constituent " building stones " may it 
be supposed that when the latter are supplied in the feed they 
may be recombined in the cells somewhat as are the amino 
acids of the simple proteins? 

No positive answer can be given to this question. It would 
seem, however, that the first steps in the autogenesis of the 
nucleoproteins must be the formation of pentoses and of the 
purin and pyrimidin bases, i.e., of precisely those substances 
which result from the digestive cleavages. Even though it be 
assumed that, in the former case, they are produced within the 
cells where they are further synthesized to nucleic acid, it is 
not altogether clear why the same substances brought to the 
cell by the blood current should not be available for the same 
purpose. Provisionally, at least, it seems perfectly possible to 
regard the entire stock of these " building stones " contained 
in the body, whether derived from the feed or produced by the 
body cells, as potentially available for the regeneration of 
nucleic acids. From this point of view, the increased excretion 
of purins which results from their ingestion would be con- 
sidered as a consequence of their increased concentration in 
the blood and as analogous to the increased excretion of urea 
which follows the ingestion of simple proteins or of amino 
acids (402). 

Katabolism 

240. Cleavages. — The katabolism of the nucleic acids 
bears a close general resemblance to that of the simple pro- 
teins. As in the case of the latter, the first general stage of the 
process consists of a series of enzymatic cleavages. These 
cleavages are quite analogous to those of the simple proteins 
and yield as final products the comparatively simple " building 
stones " of the nucleic acids. Since it is to be supposed that 
the autogenesis (238) of these compounds is via these same 



METABOLISM 1 71 

" building stones " it would appear that we have here, as in the 
case of the simple proteins, a complex of reversible enzym 
reactions. 

Phosphoric acid 
Nucleic acid ^ Pentose 

Purin or pyrimidin bases 

241. Deaminization. — The phosphoric acid which is split 
off from the nucleic acids is, of course, added to the general 
stock of this substance in the body. The pentose may be pre- 
sumed to be katabolized or possibly built up into a hexose. 

The bases, on the other hand, like the amino acids derived 
from the proteins, undergo, as the second general stage of their 
katabolism, an enzymatic deaminization and oxidation. The 
NH 2 groups are split off as ammonia and converted into urea, 
while the ring formations are largely unbroken, the principal 
end products of purin katabolism being uric acid in man and 
allantoin in most other mammals. Of the katabolism of the 
pyrimidin bases little is known. The deaminization is never 
complete, however, purin and pyrimidin bases appearing in 
the urine along with the end products of katabolism. 

242. Synthesis of uric acid. — In birds and reptiles, uric 
acid is the principal nitrogenous constituent of the semi-solid 
urine. Since no considerable portion of its nitrogen can have 
existed as preformed purins in the feed, it is evident that these 
animals must synthesize uric acid. This synthesis appears 
to take place in the liver, the antecedents probably being lactic 
acid and urea. 

§ 6. The Metabolism of the Fats 
Anabolism 

243. Resynthesis of feed fat. — In considering the resorp- 
tion of the fats (152) it was shown that, while the products of 
their digestion are glycerol and fatty acids (or their salts), 
after resorption only neutral fats have been recognized in the 
epithelial cells and in the lymph of the intestinal lacteals. 
The cleavage of the fats in digestion is reversed in the epithelial 
cells. It seems altogether plausible to ascribe this resynthesis 
to the action of an intracellular lipase, the more since the action 



172 NUTRITION OF FARM ANIMALS 

of lipase has been shown to be reversible in some cases (211). 
Whether this resynthesis be regarded as part of the process of 
resorption or be classed as one of the metabolic processes is a 
matter of indifference. In either case the material transmitted 
to the blood current consists substantially of fats. 

The digested fats are contained in the lymph in the emulsified 
form and in this state pass from the thoracic duct into the blood 
of the subclavian vein. The blood itself, however, although 
sometimes containing as much as i per cent of fat, does not 
normally carry emulsified fats, and the fat globules entering it 
from the thoracic duct do not long persist. The nature of the 
change is still uncertain ; by some, it has been regarded as a 
cleavage into fatty acids and glycerol and by others as a union 
.with proteins. But whatever the nature of the change it seems 
to be well established that the fat of the blood exists in some 
sort of combination which is soluble in water and diffusible 
and which may be called for convenience " soluble fat." 

244. Storage of fat. — A liberal supply of fat to the blood 
from the digestive tract may give rise to a storage of reserve 
fat in the adipose tissues (94) of the body. It is to be presumed 
that this deposition of reserve fat is substantially a reversal of 
the process, whatever it is, by which it was brought into solu- 
tion in the blood, the " soluble fat " of the latter passing into 
the cells and being there reconverted into the emulsified form 
and so giving rise to the globules characteristic of fat cells. 

245. Formation of cell lipoids. — The fats deposited in the 
adipose tissues, as already implied, are a store of reserve ma- 
terial, laid aside temporarily from the body metabolism when 
the feed supply is more than adequate for immediate needs. 

The various more complex lipoids (37-39, 75), however 
(cholesterins, lecithins and other phosphatids, cerebrosids, 
etc.), appear to be essential ingredients of protoplasm and to 
perform specific functions in the cell. All these substances 
have as their basis fatty acid molecules coupled with other 
groups and it is a reasonable assumption that the former are 
derived from the " soluble fat " of the blood and synthesized 
in the cells into the specific lipoids as required. 

246. Manufacture of fats. — But while the feed fats may 
serve as a source of body fats, the organism is by no means 
dependent upon the former for its supply of these substances, 



METABOLISM 1 73 

but may, as has already been indicated (217, 236), manu- 
facture fats from other ingredients of its feed. 

This view, first propounded by Liebig in 1843, was contrary 
to the opinion then prevailing and led to a lively controversy 
which, however, was definitely resolved in favor of the newer be- 
lief. Indeed, the feed fats, especially in case of herbivorous ani- 
mals, are usually of subordinate importance as sources of body fat, 
a large share of the latter being produced de now in the body. 
This fact explains in part the general uniformity of composition 
of the body fat of each species. The steer produces beef 
fat and the sheep mutton fat on substantially identical rations 
largely because the fat deposited in the body is derived only 
in small part from the feed fat, most of it being produced by the 
specific metabolic activities of the body cells. The seat of this 
synthetic production of fat, however, as well as the manner 
in which it is deposited in the reserve tissues, are still unknown. 

The sources of animal fat 

247. Experimental evidence. — The sources of animal fat 
have been already indicated. Aside from whatever feed fat 
may be stored up in the adipose tissues, the body can produce 
fat from the carbohydrates of the feed (217) and in all prob- 
ability from the non-nitrogenous residue of the proteins (236). 
In view of the historic interest attaching to the long controversy 
over this question, however, as well as of its intrinsic importance, 
an outline of the experimental evidence seems appropriate. 

That the feed fat is a source of body fat was never seriously 
questioned. When the correctness of Liebig's contention that 
the animal body can also manufacture fat had been demon- 
strated, it was assumed that the source of this new-formed 
fat was to be found in the carbohydrates of the feed and this 
was for years the accepted view. Following Liebig's termi- 
nology, the proteins were designated as the " plastic materials," 
serving to build up tissue, while the carbohydrates and fats were 
" respiratory materials," serving as sources of heat and of fat. 

248. Fat from protein. — Several earlier investigators ob- 
served facts pointing to the formation of fat from protein in 
the animal body, but Carl Voit l was the first to distinctly ad- 

1 Ztschr. Biol., 5 (1869), 79-169. 



174 NUTRITION OF FARM ANIMALS 

vocate the belief that protein constitutes an important source 
of animal fat, this conclusion being based largely on the famous 
respiration experiments of Pettenkofer and Voit at Munich in 
which a dog was fed lean meat freed from visible fat as carefully 
as possible (this being the nearest practicable approach to a 
pure protein diet) and the balance of nitrogen and carbon 
(287, 292) determined. The results showed in many cases a 
retention of carbon by the animal greater than corresponded to 
the quantity of protein gained, and this difference was inter- 
preted, according to the methods described in Chapter VI 
(293) , as showing a production of fat. 

Pettenkofer and Voit's experiments were long accepted as 
conclusive until Pfliiger 1 subjected them to destructive criti- 
cism, showing the possibility of material errors in the estimates 
of the carbon of both feed and visible excreta. 

It scarcely need be said that this result does not prove that 
fat is not formed from protein, but simply that Pettenkofer and 
Voit's experiments fail to demonstrate it. Of later experi- 
ments on the subject, a number seem to show clearly the for- 
mation of a small amount of fat from protein, even after every 
allowance has been made for the objections raised by Pfliiger 
in his criticisms of the experiments. A number of negative 
results have, it is true, also been reported, but naturally nega- 
tive results are of much less value than positive ones. 

Moreover, the indirect evidence in favor of the possibility 
of the formation of fat from protein seems practically conclu- 
sive. As already stated (235), it has been established beyond 
reasonable doubt that carbohydrates may be produced from 
protein in the body. If this is true, however, it almost neces- 
sarily involves the possibility of the formation of fats from pro- 
tein, since carbohydrates are undoubtedly a source of fat. 

249. Fat from carbohydrates. — Pettenkofer and Voit, 2 how- 
ever, went further than to demonstrate, as they believed, the 
formation of fat from protein. Their experiments included a 
number in which carbohydrates were added to a ration of 
protein (lean meat). Assuming with Henneberg 3 that ioo 
grams of protein might yield 51.4 grams of fat, they computed 
that all the fat produced by the animal in these experiments 

1 Arch. Physiol. (Pfliiger), 51 (1892), 229. 

2 Ztschr. Biol., 9 (1873), 435. 3 Landw. Vers. Stat., 10 (1868), 455. 



METABOLISM 



J 75 



could, with only one or two exceptions, be accounted for by the 
fat and protein of the feed. They, therefore, characterized the 
formation of fats from carbohydrates as improbable. The some- 
what general impression that Voit absolutely denied the pro- 
duction of fat from carbohydrates is incorrect, although he re- 
garded it as improbable and unproved. Indeed, he came later to 
admit the truth of the opposite view and even furnished from 
his own laboratory experimental evidence in its support. Never- 
theless, his earlier opinion as to its improbability obtained wide 
currency and in the hands of his followers became almost a 
dogma, so that protein was given a vital and preponderant im- 
portance the effect of which has been unfortunate both for the 
development of the science of nutrition in general and upon the 
theory of stock feeding in particular. 

Henneberg's estimate of the maximum fat production from 
protein was soon virtually accepted as an established fact and 
with the use of this high figure it was easy to compute from most 
of the experiments on fat production then on record that the fat 
and protein of the feed were sufficient to account for the fat 
produced. Similar computations upon a large number of later 
feeding experiments l yielded similar results, so that belief in 
the non-formation of fat from carbohydrates was further 
strengthened. 

One notable exception to the rule, however, were the experi- 
ments made by Lawes and Gilbert in 1850 upon the fattening of 
swine. These were comparative slaughter tests (284) in which 
the gain of fat was determined by comparing the weight and 
composition of similar animals, one before and the other after 
fattening. They were, accordingly, subject to a somewhat 
considerable range of error, but even on the most extreme as- 
sumptions it was impossible in six out of the nine experiments 
to account for the fat actually produced by the supply of fat 
and protein in the feed. These investigators, therefore, con- 
tinued to maintain, in spite of much adverse criticism, the 
formation of fat from carbohydrates, although their experi- 
ments hardly secured the recognition which they deserved. 

As time went on, however, results began to accumulate which, 
like Lawes and Gilbert's showed a much larger production of 
fat than could possibly be ascribed to the fat and protein of 

See the author's Manual of Cattle Feeding, p. 177. 



176 NUTRITION OF FARM ANIMALS 

the feed. This was particularly the case as it came to be more 
clearly recognized that Henneberg's estimate of a production 
of 51.4 grams of fat from 100 grams of protein was in all prob- 
ability too high, and especially after it was shown that what 
had been regarded as digested protein in many of these experi- 
ments (i.e., digestible N X 6.25) consisted in part of much 
simpler nitrogenous compounds. The ready formation of 
fat by the hog rendered this animal a very suitable subject for 
experiment, and the great majority of investigations on this 
animal have supported the view that fat is produced from 
carbohydrates, but similar results upon other species have not 
been lacking, while respiration experiments upon swine, geese, 
dogs, and especially the extensive investigations by G. Kiihn l 
upon cattle have completed the demonstration. 2 

In the light of all these results, the formation of fat from 
carbohydrates in the animal body is now universally admitted, 
while its production from protein is still questioned by a few 
and in any case is of little economic significance, so that we 
have come back by a curious reversal of views almost to Lie- 
big's classification of the nutrients into plastic and respiratory. 

This conclusion applies specifically to the pure hexose carbo- 
hydrates, particularly starch. In many of the experiments 
cited, however, the non-nitrogenous material digested by the 
animal consisted to a not inconsiderable extent of those sub- 
stances of uncertain chemical nature included in the terms 
crude fiber and nitrogen-free extract. Postponing for the 
present any discussion of the nutritive value of these groups, 
it may suffice to say here that Kellner's investigations 3 in 
particular show that both of them, including the pentosans, may 
serve as sources of fat. 

Katabolism 

250. Body fat a reserve. — The stored fat of the adipose tis- 
sues, aside from its mechanical functions, constitutes the great 
reserve of energy-yielding material in the body. In the lack of 
an adequate feed supply, common observation shows that this 

1 Kellner : Landw. Vers. Stat. ; 44 (1894), 257. 

2 Compare the author's Principles of Animal Nutrition, pp. 165-184. 
3 Landw. Vers. Stat.; 51 (1900). 



METABOLISM 1 77 

reserve is drawn upon for the support of the internal activities 
of the body and as a source of energy for the performance of 
external work. 

251. Mobilization of reserve fat. — In order that the stored 
fat may be used for the general metabolism of the body it 
must first be transferred from the adipose tissue cells to the 
localities where it is needed. Presumably this is accomplished 
by its reconversion into " soluble fat " and its passage through 
the walls of the cells into the blood, that is, by a reversal of 
the process by which it was laid down. Since the transfer of 
fat through the epithelial cells in resorption is effected by a 
hydrolytic cleavage (152), one is tempted to, imagine a similar 
reversible enzymatic process in this case. Direct evidence of 
this is lacking, but apparently such a cleavage takes place some- 
where at an early stage in the katabolism of the fats, the re- 
sulting glycerol perhaps serving as a source of dextrose. From 
that point on the katabolism is that of the fatty acids. 

252. Oxidation at the p carbon atom. — The oxidation of the 
fatty acids, either saturated or unsaturated, to carbon dioxid 
and water, like the other katabolic processes already considered, 
is a step by step process. The researches of Knoop, Embden, 
Dakin and others 1 have rendered it highly probable, if not cer- 
tain, that the oxidation, at least in the case of the normal satu- 
rated acids, begins at the /3 carbon atom (i.e., at the second 
carbon atom from the COOH group) and results in the splitting 
off of two carbon atoms at a time. The products are carbon 
dioxid, water and a fatty acid containing two less carbon 
atoms than the original one and with which the same process 
of erosion is repeated. 

If it be true that the fatty acids thus undergo katabolism in 
the body by stages of two carbon atoms each, and particularly 
if it may be regarded as probable that they may be built up 
again in a similar manner from simpler atomic chains, there 
is afforded a plausible explanation of the rather striking fact 
that nearly all of these compounds found in the animal body 
contain an even number of carbon atoms. 

This scheme does not provide for the oxidation of the three 
lower acids of the series, propionic, acetic and formic, and in 

Compare, Dakin, Oxidations and Reductions in the Animal Body, 191 2, pp. 
I7-47- 

N 



178 NUTRITION OF FARM ANIMALS 

fact, while these acids are known to be freely oxidized in the 
body, the chemical mechanism of the process is little under- 
stood. 

253. Formation of carbohydrates from fats. — In discussing 
the probability of the formation of carbohydrates from pro- 
teins (235), it was pointed out that their origin might often be 
ascribed to either proteins or fats or both. It was there shown 
that in many cases the probabilities strongly favored a forma- 
tion from proteins. In other instances, however, the proba- 
bilities seem equally strong that fats give rise to carbohydrates. 
In particular, experiments upon phloridzin diabetes of the 
dog have shown the production of more sugar than could be 
formed from the quantity of protein katabolized during the 
same time, while the stock of glycogen in the animals experi- 
mented on had been so exhausted by fasting and muscular work 
that it seems scarcely possible to interpret the results ' other- 
wise than as showing the formation of sugar from fat. It should 
be added, however, that it has been seriously questioned whether 
the conditions of the experiments were sufficiently controlled 
to warrant the conclusions drawn. 

The very low values for the respiratory quotient (296) which 
have been reported in some cases for hibernating animals have 
also been interpreted as indicating a production of carbohydrates 
from fat. In the conversion of fat into sugar, there must ob- 
viously be an absorption of oxygen with no corresponding evolu- 
tion of carbon dioxid, the tendency of which would be to lower 
the respiratory quotient. The value of the latter for the direct 
oxidation of fat is 0.7. In hibernating animals, however, 
figures as low as 0.3 have been reported, while the weight of the 
fasting animal increased. While these facts, of course, do not 
demonstrate the formation of sugar from fat, they are quite 
compatible with that interpretation and seem to indicate a 
storage of oxygen. The more recent experiments on hibernat- 
ing animals, however, have failed to give such low quotients as 
were obtained by earlier observers. 

§ 7. Metabolism of Ash Ingredients 

254. Certain chemical elements of the body and of the feed 
are found wholly or in part in their ash when these materials 



METABOLISM 1 79 

are burned and are therefore spoken of as ash ingredients, al- 
though, as already pointed out (3, 5), this does not necessarily 
imply that they existed in the original material in " inorganic " 
combination. Most of these elements are as essential to the 
vital processes as the more abundant elements carbon, nitro- 
gen, hydrogen and oxygen of the so-called " organic compounds," 
although unfortunately the laws regulating their metabolism 
have been much less extensively studied. Among these ele- 
ments sulphur and phosphorus are of special importance in 
this connection. 

Sulphur 

255. Sources. — While feeding stuffs may contain small 
amounts of sulphur in the form of sulphates, by far the greater 
part of this element in the feed of animals exists in organic 
compounds. Such, for instance, are the allyl sulphid (CsHs^S, 
contained in garlic and other members of the genus allium, and 
the allyl sulphocyanat, C3H5 • CNS, found in mustard and other 
genera of the cruciferse. Ordinarily, however, the chief car- 
riers of organic sulphur, both in feeding stuffs and animals, 
are the proteins, which contain the element in the form of the 
di-amino acid cystin (47). 

256. Katabolism. — The question whether the animal body 
can build up its sulphur compounds from inorganic sulphur 
does not appear to have been investigated. 

The katabolism of the cystin component of proteins pre- 
sumably follows the same general course as that of the other 
amino acids, i.e., it is split off from the proteins by hy- 
drolytic cleavage and subsequently deaminized. One of the 
products of the katabolism of cystin appears to be taurin, 
CH2 • NH 2 • CH 2 • SO3H, contained in the taurocholic acid of the 
bile. To the extent, therefore, to which the latter com- 
pound escapes resorption in the lower intestine, it carries small 
amounts of sulphur into the feces. Both cystin and taurin, 
however, are readily oxidized in the body, the larger part of 
their sulphur taking ultimately the form of sulphuric acid and 
being excreted in the urine. The sulphuric acid of the urine 
exists in combination in part with aromatic radicles derived 
from the putrefaction of the proteins in the lower intestine 
and in part with bases. In human urine about one-fifth of 



l8o • NUTRITION OF FARM ANIMALS 

the total sulphur exists in a less completely oxidized form 
known as neutral sulphur, the nature and origin of which is 
obscure. 

Phosphorus 

257. Forms ingested. — The phosphorus supply of the body 
is received substantially in the four forms indicated in Chapter 
I (5), viz., as phosphates, as phosphatids, as phospho- and 
nucleo-proteins and as phytin. Of these the various " organic " 
forms usually predominate. 

It appears probable, however, that all these various forms of 
phosphorus are resorbed into the blood stream in the form of 
phosphoric acid. Of the phosphates ingested as such this is 
certainly true. There seems good reason for believing that the 
phosphoric acid radicle contained in the nucleic acid of the 
nucleoproteins is quite completely split off by the digestive 
enzyms and reaches the blood as phosphoric acid (139), and 
the same thing is presumably true of the phosphoproteins. 
The phosphatids are probably acted on by the lipases of the 
digestive tract, but whether the glycerophosphoric acid resulting 
from their cleavage is further split up is unknown. The ready 
cleavage of phytin in seeds would suggest that probably its 
phosphorus also is resorbed as phosphoric acid. 

258. Anabolism and katabolism. — The animal body contains 
a large store of phosphorus in the " inorganic " form, especially 
in the skeleton. For the maintenance or increase of this store 
the resorbed phosphoric acid is naturally available. 

The body also contains, however, organic phosphorus com- 
pounds, which, although less in amount than the inorganic, 
are of the highest significance for the vital functions. The be- 
lief that the phosphorus supply of the body is resorbed chiefly 
in the form of phosphoric acid necessarily implies, therefore, 
that the organism is able to utilize inorganic phosphorus for the 
synthesis of nucleic acids, phosphoproteins, phosphatids, etc., 
and the experimental evidence is strongly in favor of this 
belief (497). In this respect, as in many others, the synthetic 
power of the organism appears to be greater than was long 
supposed. 

Little is known regarding the course followed by the phos- 
phorus in the katabolism of the nucleoproteins, phosphatids, 



METABOLISM 181 

etc. Ultimately it takes the form of phosphoric acid and is 
excreted in the feces or urine (199), but whether any inter- 
mediate compounds are formed is not known. 

Other elements 

While the other so-called ash ingredients are no less impor- 
tant than the two just considered, little is known regarding their 
katabolism in the ordinary sense, i.e., of the chemical changes 
which they undergo in the body. That they may exist in 
feeding stuffs in organic as well as in inorganic forms is probable. 
That they enter into organic combination in the animal body is 
likewise to be assumed but is positively known in only a few 
instances like that of the iron of the haemoglobin and the 
iodin of the thyroid glands. 

259. Sodium and potassium. — Both sodium and potassium 
are contained in the ordinary foods and feeding stuffs and in 
addition man and farm animals consume not inconsiderable 
amounts of common salt, although it appears probable that this 
serves to a considerable extent as a condiment and that the 
amount actually necessary is less than is often supposed. Bab- 
cock, e.g., was able to keep cows for over a year without access 
to salt, except that contained in their feed, without any obvious 
ill consequences. 

Both potassium and sodium, as well as the chlorin com- 
bined with the latter in the form of salt, are excreted in the 
urine. 

260. Calcium and magnesium. — These elements, calcium in 
particular, are especially important in their relations to the 
growth and maintenance of the skeleton, but they are not lacking 
in the soft tissues also, where they perform important functions. 
Of their intermediary metabolism little is known. As noted 
in Chapter IV (199), the normal path of excretion of calcium, 
and to some extent of magnesium, is through the lower in- 
testine, so that the apparent digestibility of these elements is 
no measure of the amount actually resorbed and utilized in the 
body processes. 

261. Iron. — A long controversy has been carried on over 
the question whether inorganic iron may be resorbed and if so 
whether it can be utilized for the synthesis of the haemoglobins 



l82 



NUTRITION OF FARM ANIMALS 



and for other purposes in the body. Both questions, however, 
may be regarded as settled in the affirmative. The matter is 
of importance in its relations to the use of iron in medicine but 
is of no special significance in stock feeding. 

The excretion of iron takes place almost exclusively through 
the intestines and this fact led to the earlier conclusion that 
inorganic iron cannot be resorbed. 



§ 8. Functions of the Nutrients 

262. General scheme of metabolism. — In considering the 
metabolism of the several classes of nutrients in the foregoing 
paragraphs, it was found that the main features of the process 




Fig. 23. — Diagrammatic scheme of metabolism. 

in each case might be conceived of in accordance with the ideas 
suggested in § 2 (210-212) as consisting of a complex of rever- 
sible reactions accelerated or retarded by intracellular enzyms. 
By combining the equations used to represent those reactions, it 
appears possible to take a further step and formulate the fol- 
lowing highly generalized scheme for the total metabolism which 
may serve to show the interrelations between the metabolism 



METABOLISM 183 

of the chief classes of organic nutrients. For the sake of sim- 
plicity some of the intermediate steps mentioned on previous 
pages have been omitted. The central portion of the diagram 
includes the feed substances taken up into the blood. At the 
extreme left are shown the main groups of tissue ingredients, 
and at the extreme right the excretory products. 

It cannot be too strongly emphasized that any such diagram 
as the foregoing is of necessity in the highest degree schematic. 

For one thing, neither the enzymatic nature nor the revers- 
ibility of the changes indicated in the diagram has been estab- 
lished except in a few cases. As already pointed out (212), 
this conception of the nature of metabolism is still to a large 
extent hypothetical, although the hypothesis harmonizes well 
with the present state of our knowledge. 

Moreover, aside from the mere omission from the diagram of 
certain recognized products of the intermediary metabolism, 
the chemical processes in the body are doubtless infinitely more 
complex than can be indicated in any such way. A vast num- 
ber of different substances have been identified in the animal 
body, many of which are known to have important functions 
in keeping the organism in running order but which are not 
even hinted at in this scheme. 

In brief, the scheme is concerned with the results of the 
metabolic processes so far as they are related to nutrition 
rather than with the mechanism by which these results are 
brought about. It seeks to show in outline how the principal 
groups of nutrients are related, on the one hand, to the building 
up of body tissues, and, on the other hand, to the formation of 
excretory products, and to indicate the mutual relations of the 
several groups. For this purpose it may perhaps serve a use- 
ful end as an aid to memory, provided its limitations are clearly 
understood. 

263. Dual function of feed. — As pointed out in § 1 of this 
chapter (207), the animal body may be regarded in the light of 
a transformer of energy. By the agency of the protoplasm of 
its cells, in ways largely hidden from us, it converts the chemical 
energy supplied in its feed into the various forms characteristic 
of living matter. From this point of view the feed has a two- 
fold function. 

First, the feed ingredients are carriers of energy. The higher 



1 84 NUTRITION OF FARM ANIMALS 

plants transform the radiant energy of the sun into the chemical 
energy of their various constituents, to be yielded up by the 
latter to the animal organism through the processes of metab- 
olism. This conception has become a familiar one and much 
emphasis has been laid upon it in recent years. 

Second, the feed supplies the specific materials required for 
building and maintaining all the complex structures of the 
body and for their harmonious functioning, i.e., it is the source 
of structural and repair material. 

That the proteins, fats and mineral ingredients which make 
up by far the larger part of the dry matter of the body (99, 280) 
are derived ultimately from the feed needs no special demon- 
stration, but the importance of many substances present in the 
body in only minute amounts tends to be overlooked. For 
example, the enzyms of the body, both extra- and intra-cellular, 
form no considerable portion of its mass, yet they are essential 
to its vital activities. So, too, the various hormones and se- 
cretions of the ductless glands, while ignored in the broad scheme 
of metabolism just presented, are essential to the vital processes. 
Clearly, the feed must supply material for the production of 
these and other similar substances. 

In other words, no amount of energy-yielding material will 
suffice to support life in the absence of those specific substances 
which are necessary in order that the machinery of conversion 
shall operate properly, much as no amount of coal under the 
boiler will enable an electric plant to furnish a normal amount 
of current if the insulation of the generator is defective. For 
example, if tryptophan is necessary for the formation of some 
essential internal secretion, a diet lacking that substance, 
however much energy it might furnish, would fail to support the 
organism permanently unless the body can manufacture trypto- 
phan from other substances. 

The latter qualification is a very important one. The animal 
is very far from being dependent upon the presence in its feed 
of all the varied chemical compounds required for its operation. 
Indeed, quite the reverse is the case. As has appeared in pre- 
vious sections, the actual substances resorbed are comparatively 
simple and uniform and upon them the animal body executes 
a great variety of chemical changes, both analytic and synthetic. 
What is necessary is that the resorbed feed shall include sub- 



METABOLISM 185 

stances out of which the body can manufacture the compounds 
which it requires. 

264. Functions of the proteins. — The proteins furnish at 
once the most familiar and the most striking example of this 
dual function of the feed. 

Since the proteins may be katabolized in the body with the 
formation of products (carbon dioxid, water, urea, etc.) con- 
taining either no available energy or but a small fraction of 
that found in the original proteins, it is clear that the latter 
serve as carriers of energy. In fact, it has been shown to be 
possible to maintain a carnivorous animal in normal activity 
for an indefinite time on a diet containing substantially nothing 
but protein as a source of energy. 

But proteins serve also as building material. Aside from 
water, the working machinery of the body is composed largely of 
proteins, while very many at least of the special substances 
already mentioned are nitrogenous and probably derived from 
the proteins. These protein tissues and other substances must 
be built up in the growing animal and maintained in the mature 
one, and for this purpose only proteins or their cleavage prod- 
ucts can be utilized, and their presence in the feed is indis- 
pensable. 

A point which sometimes causes perplexity is that the same 
portion of protein may not only serve as structural material 
but also yield energy for the vital processes, so that in esti- 
mating the energy supplied by a feeding stuff that of its protein 
as well as that of its other ingredients is included. The difficulty 
disappears, however, when it is remembered that any given 
portion of protein does not perform both these functions at the 
same time. If a gram of protein in the feed of a mature animal 
is used for structural purposes it practically takes the place of 
an equal amount of tissue protein, while the latter is katabolized 
and yields substantially the same amount of energy as would 
have been available from the gram of feed protein had that 
been katabolized instead. The latter, with its store of energy, 
has been temporarily set aside from the katabolic process but at 
some later time may itself be replaced by another gram of feed 
protein and katabolized in its turn, liberating the corresponding 
amount of energy. The repairing of a wooden building may 
serve as an illustration. The old wood taken out to make way 



1 86 NUTRITION OF FARM ANIMALS 

for new material, as well as any surplus of new wood over that 
immediately required, may be used indifferently as fuel for 
warming the building. The case of the young animal, in which 
protein is permanently set aside for growth, is a trifle more com- 
plex but substantially the same considerations hold good. 

265. Functions of fats. — In the case of the fats the energy- 
bearing function is the predominant and obvious one. Fats 
are a concentrated form of fuel, containing much more energy 
per unit than any of the other nutrients. They supply much 
energy in a small bulk and are, therefore, well adapted for the 
storage of reserve energy in the body. 

The fats and closely related bodies (the lipoids), however, 
are also important and apparently essential constituents of 
protoplasm (75). The lipoids, therefore, have important 
structural functions and an adequate supply of them in the 
body is indispensable. From this point of view, some interest 
attaches to the results obtained by a number of investigators 
who claim to have shown that a certain minimum supply of 
lipoids in the feed is essential, especially for growing animals. 
The evidence, however, is negative evidence, i. e., experimental 
animals failed to grow normally on a lipoid-free diet. In view 
of the positive results obtained by Osborne and Mendel, 1 as well 
as of the fact that both the simple fats and the phosphatids, at 
least, can be synthesized freely in the organism, and taking into 
consideration the extensive synthetic power of the body in 
general, it is difficult to believe that the presence of lipoids in 
the feed is indispensable, and more recent investigations have 
afforded a different explanation of the observed facts (498) . On 
the other hand, it has been shown that the lecithins stimulate 
growth and also that the fats appear, within certain limits, to 
favor the production of milk fat. 

266. Functions of carbohydrates. — The carbohydrates even 
more distinctly than the fats serve chiefly as carriers of energy. 
While containing less energy per unit than fats, they can, on 
the other hand, be consumed in larger quantities and they 
practically supply the greater part of the energy in the diet of 
man and of farm animals. While the presence of carbohydrates 
(dextrose) in the blood and lymph is essential, this appears to 
be chiefly on account of their ready availability as fuel material. 

1 Jour. Biol. Chem., 12 (1912), 81. 



METABOLISM 1 87 

The carbohydrates seem, however, to have a specific function 
in relation to the katabolism of fats. When the body is com- 
pelled to draw its energy supply chiefly from the fats, as in 
fasting or in diabetes (in which the power of katabolizing car- 
bohydrates is lost), or when carbohydrates are absent from the 
diet, the katabolism of the fats fails to be complete and con- 
siderable amounts of beta-oxybutyric acid as well as the ab- 
normal katabolic product aceton are excreted unoxidized in the 
urine. 

267. Non-nitrogenous nutrients in general. — While it thus 
appears that both the fats (or lipoids) and carbohydrates may 
serve special purposes in the body, it is, nevertheless, clear 
that their chief function is to supply energy. Their amounts in 
ordinary rations are so abundant that as compared with their 
functions as carriers of energy any specific purposes which 
they serve in the body are amply provided for. As related to 
the nutrition of farm animals in particular, it is of special 
interest to note that not only the fats and carbohydrates di- 
gested as such but also the products of the bacterial fermenta- 
tion of the insoluble carbohydrates are available as sources of 
energy. 

268. Functions of ash ingredients. — While the non-nitroge- 
nous organic nutrients serve chiefly as carriers of energy and 
only in a minor degree to provide the compounds necessary for 
the performance of specific bodily functions, the so-called ash 
ingredients represent the other extreme in this respect. They 
introduce practically no available energy into the organism but, 
on the other hand, they are not only essential structural com- 
ponents of the body tissues but likewise supply and maintain 
certain conditions indispensable to the performance of the 
bodily functions. 

The structural importance of the ash ingredients is most 
manifest in the case of the skeleton, which, in the higher ani- 
mals, contains relatively large amounts of calcium and phos- 
phoric acid and small quantities of magnesium, sodium and 
carbonic acid (81) which impart to it certain necessary me- 
chanical qualities of strength and rigidity. The necessity for 
a supply of these substances in the feed, especially in that of 
growing animals, is too obvious to require discussion. The 
ash ingredients, however, have other equally important functions 



1 88 NUTRITION OF FARM ANIMALS 

in providing the necessary conditions for the chemical and physi- 
cal activities of the various tissues. 

269. Osmotic pressure. — The cells of the various tissues 
draw their nourishment from the lymph which constitutes their 
immediate nutritive environment (185) and from which they are 
separated by cell walls which partake of the nature of semi- 
permeable membranes. In order to maintain normal condi- 
tions in the protoplasm of the cells the osmotic pressure of the 
lymph, and therefore that of the blood from which it is derived, 
must be maintained approximately constant. The osmotic 
pressure of the blood is stated to be approximately about 8 
atmospheres, due largely to the ash ingredients contained in 
solution. With an adequate supply in the feed the concen- 
tration of mineral matter in the blood is regulated chiefly by 
the excretory activity of the kidneys. Thus, in the case of 
sodium chlorid, for example, it is estimated that the blood of 
an average man contains approximately 30 grams of this sub- 
stance, of which hardly half a gram is excreted daily when 
none is consumed. If, however, salt is added to the diet, the 
excess is promptly excreted in the course of the next twenty- 
four hours. What is true of salt in this respect is true also of 
other diffusible ingredients of the blood. 

270. Ionic concentration. — The variqus salts are contained 
in the body largely in dilute aqueous solution. In such solu- 
tions, however, it is believed that salts are largely dissociated 
into their constituent ions, a dilute solution of common salt, 
for example, containing in addition to some unchanged NaCl 
the ions Na and CI, one of calcium sulphate the ions Ca and 
SO4, etc. Acids are similarly dissociated, yielding hydrogen 
ions (H2SO4 ^H + SO4), while alkalies yield OH ions 
(KOH ^ K + OH) . Some of these ions have been shown to 
have specific effects on certain cellular activities. For example, 
a frog muscle kept in 0.7 per cent NaCl solution retains its irrita- 
bility for one or two days. In a solution of a non-electrolyte, 
like sugar, asparagin, etc., having the same osmotic pressure, the 
muscle soon loses its irritability, but if NaCl be added to the 
solution it regains it. Since a number of other sodium salts 
produce the same effect, while chlorids of other metals do not, 
it is apparent that the effect is due to the Na ions. On the 
other hand, Na ions alone cause long continued rhythmic con- 



METABOLISM 189 

traction of muscles, which, however, is suspended by the pres- 
ence in the solution of certain (not all) dyad ions like Ca or Mg. 
Numerous other examples of such antagonistic actions of ions 
are known, such as those observed by Loeb, for example, in 
the development of the egg. In general it may be said that cell 
activities are dependent among other things upon a suitable 
ionic concentration of various elements in their surroundings, 
and it is a striking and interesting fact that the so-called physi- 
ological salt solutions in which living organs may be kept func- 
tionally active for a longer or shorter time contain the various 
salts in approximately the same proportions as are found in 
sea water. 

Another example of the influence of ionic concentration is 
afforded in the case of the digestive enzyms. Ptyalin, for 
example, is sensitive to a very slight excess of hydrogen ions. 
Pepsin, on the other hand, is most active in the presence of 
hydrogen ions, while trypsin acts best in the presence of an 
excess of OH ions. 

271. Maintenance of neutrality. — Closely connected with 
the foregoing topic and constituting indeed a special case of it, 
is that of the maintenance of neutrality in the body fluids. A 
fluid is neutral in the chemical sense when it contains 
no excess of H nor of OH ions, an excess of the former being 
equivalent to acidity and an excess of the latter to alkalinity. 
It has been shown that the blood serum, as a representative of 
the body fluids, is very nearly neutral, its content of H and 
OH ions being approximately 0.4 X io -7 and 7.2 X io -7 , 
i.e., it has an alkalinity equivalent to about 0.000012 gram 
NaOH per liter. 1 

The body katabolism is continually producing acids, espe- 
cially carbonic, phosphoric and sulphuric acids (256, 259), which 
tend to increase the acidity of the blood. These acids are in 
part neutralized by the ammonia produced in the katabolism of 
protein (233), but it has been shown by the investigations of 
L. J. Henderson that the salts of the blood serum, especially 
the sodium phosphates and bicarbonates, play an important 
part in maintaining its neutrality. They are present in such 

1 Blood is commonly said to be alkaline because it gives an alkaline reaction to 
ordinary indicators, such as litmus. Such a reaction, however, gives no definite 
measure of the true alkalinity or acidity. 



190 NUTRITION OF FARM ANIMALS 

proportions that their solution possesses nearly the maximum 
capacity for the preservation of neutrality, while they also, 
particularly the phosphates, serve as a means of elimination of 
an excess of acid through the kidneys in the form of the acid 
phosphates of the urine. 

272. Other functions of ash. — The three general functions 
just enumerated by no means exhaust the list of offices performed 
by the ash ingredients. Iron, for example, is an essential in- 
gredient of haemoglobin, the coloring matter of the red blood 
corpuscles, which is the vehicle by which oxygen is distributed 
throughout the body (191). Although contained in the body 
in relatively minute amounts, this element is, therefore, one of 
prime necessity. Iodin appears to be an essential ingredient 
of the thyroid glands, and although we are ignorant of its 
exact functions it is known that the absence of these glands, or 
their failure to function, gives rise to serious disturbances 
(goitre, myxcedema). Recent investigations seem to indi- 
cate that manganese and boron, and perhaps other elements 
not heretofore regarded as essential, may have important 
functions as catalysts in plants and perhaps, therefore, in 
animals also, although this is at present a conjecture. It is 
likewise possible that other elements present in small amounts 
may later be shown to have physiological functions. 

273. Functions of water. — Its very familiarity tends to make 
us overlook the striking nature of the fact that life as we know 
it is impossible in the absence of water. If protoplasm may be 
regarded as a collodial solution, one may almost say that life 
is possible only in aqueous solutions. 

Some reasons for this are fairly obvious. The phenomena of 
osmotic pressure and ionization, for example, whose impor- 
tance has just been indicated, are substantially solution phe- 
nomena. It is possible also that there are more fundamental 
reasons for this striking fact. Certainly the larger share of our 
present chemical knowledge relates to the chemistry of either 
aqueous solutions or gases, two states resembling each other 
in many respects and in which chemical action seems to occur 
most readily, if indeed it ever takes place in the solid state. 
Moreover, it has been shown that some reactions, at least, in 
which water is not commonly regarded as concerned, are 
dependent upon the presence "of minute amounts of this sub- 



METABOLISM 1 91 

stance, or at least proceed with extreme slowness in its absence. 
Such, for example, is the action of chlorin on metallic copper 
or iron, or of oxygen upon many of the elements even at high 
temperatures. 

Aside from these considerations, however, the importance of 
the part played by water in the animal economy is sufficiently 
obvious, while it constitutes in most cases more than half of 
the weight of the body (97) and therefore may be regarded 
as having structural importance. 



CHAPTER VI 
THE BALANCE OF NUTRITION 

§ i. General Conception 

274. The animal as a prime motor. — The living animal 
constitutes what is known as a prime motor ; that is, it gener- 
ates power for its own operation and is able to produce a surplus 
which may be applied to do external work. In particular, a 
fairly close analogy may be drawn between the animal body and 
what are known as internal combustion motors. In such motors, 
a fuel (gas, gasoline, alcohol, etc.) is burned in the cylinder of 
the engine itself and its available chemical energy is transformed 
in part into motion and in part into heat. In a somewhat 
similar manner the compounds supplied to the cells of the body 
by the processes of digestion, resorption and circulation are 
katabolized, combine with the oxygen introduced through the 
lungs, and yield energy for the various activities of the organism. 
It should be noted that these activities include not merely ex- 
ternal work done by the animal but likewise a variety of internal 
work, such as that of circulation, respiration, digestion, resorp- 
tion, secretion, etc. In other words, the animal machine is 
always in operation, even when performing no external work. 

275. Expenditure by the body. — When in operation, a me- 
chanical prime motor (a gasoline engine, for example) consumes 
two things. First, the material of which the working parts are 
composed is gradually worn away so that ultimately repairs 
are necessary, and second, fuel is consumed in amount depend- 
ing upon the work done. Substantially the same thing is true 
of the animal body. 

The working machinery of the body may be regarded as 
composed essentially of water, ash and protein. This ma- 
chinery, like that of the engine, is continually wearing out ; that 
is, the protein in particular is being continually katabolized and 

IQ2 



THE BALANCE OF NUTRITION 193 

the products of its oxidation excreted. In addition, the activi- 
ties of the body, like those of the engine, require a supply of 
fuel material containing available chemical energy equivalent 
to the work to be done. For this purpose the body utilizes 
in the first instance the substances contained in its own cells 
and tissues. As shown in Chapter V, all the organic ingredients 
of the body — protein, fat and carbohydrates — undergo 
katabolism, giving rise to carbon dioxid, water and compara- 
tively simple nitrogenous products, accompanied by a trans- 
formation of their chemical energy into other forms. In other 
words, the body is a storehouse of chemical energy as well as a 
mechanism. This stored-up energy of the body is contained 
particularly in its fat, and to a minor degree in its glycogen, 
while the body protein, although it likewise yields energy when 
katabolized, especially through the oxidation of its non-nitrog- 
enous residue (229), usually plays a small part quantitatively. 
The fat of the body constitutes its great reserve of energy. The 
store of reserve material in the body may be compared, for the 
sake of illustration, to the gasoline in the tank of an automobile, 
with the difference, however, that the body derives more or 
less energy from the combustion of the material (protein) of 
the engine itself. 

276. The feed. — Neither the automobile nor the animal can 
long depend entirely upon its own stock of material without 
disaster. Sooner or later it must obtain supplies from the out- 
side. The supplies required in both cases are obviously of two 
classes, corresponding to the two classes of materials consumed 
in the operation of the machine, and may be briefly designated 
as repair material and fuel. 

In the automobile, parts of the machinery, the tires, etc., as 
they wear out must be replaced by new ones of the same kind, 
while the gasoline tank must be filled at intervals and the work- 
ing parts must be suitably lubricated. The case of the animal 
is precisely similar. In the first place, it must be supplied in 
its feed with materials from which, by the processes of digestion 
and resorption, it can secure the particular atomic groupings 
(amino acids, peptids, ash ingredients, etc.) which will exactly 
fit into its protoplasm and replace those eliminated by the vital 
activities. In the second place it must also derive from its 
feed molecules which it may, according to circumstances, break 



194 NUTRITION OF FARM ANIMALS 

down (katabolize) at once for the sake of their energy or store 
up as a reserve of energy (fat, glycogen) for future use. Finally, 
to carry the analogy a step further, it must obtain from its feed 
such amounts and proportions of the several ash ingredients 
as will maintain the necessary working conditions of osmotic 
pressure, ionic concentration and the like, somewhat as the 
engine must be lubricated. 

277. Balance of income and expenditure. — It is evident 
from the foregoing considerations that the body exhibits two 
sets of activities, those concerned in its actions as a prime 
motor, tending to destroy it, and those of nutrition, tending to 
build up and increase it. Whether the body gains, is main- 
tained or falls away depends upon the balance between these 
two sets of activities. 

In a broad general way, of course, this fact is perfectly obvious. 
We do not need a physiologist to teach us that the horse or cow 
cannot long continue to do work or to yield milk unless supplied 
with sufficient feed to make good the resulting loss of body 
material. Similarly, we are familiar with the fact that those 
operations of the body which go on in a state of so-called rest 
likewise require material for their support, so that the mere 
maintenance of an animal calls for an expenditure of feed. 
What is needed in a scientific study of nutrition is something 
more than the mere general knowledge of these familiar facts ; 
namely, a quantitative measure of the extent to which the 
various feeding stuffs or their single ingredients contribute to 
the nutritive functions of the body under varying conditions. 

§ 2. Methods of Investigation 

278. Investigation of details of metabolism. — One method 
of attacking the problem just stated is by investigating the 
details of the metabolic processes. In the study of metabolism 
(including the chemical changes in digestion and resorption) 
the attempt is made to follow the various ingredients of the feed 
through the body and to trace in detail how, where and to what 
extent they contribute to the maintenance or growth of tissue 
or supply energy for the use of the organism. Such studies are 
of fundamental importance. They reveal to us how the animal 
mechanism operates. When carried to their ultimate con- 



THE BALANCE OF NUTRITION 1 95 

elusion, and when accompanied by a complete knowledge of 
the chemical ingredients found in feeding stuffs, they will make 
it possible to give an exhaustive account of nutrition as a physico- 
chemical process. It is hardly necessary to say that the reali- 
zation of this ideal lies in the distant future. 

279. Total nutritive effect. — Meanwhile, students of stock 
feeding are interested primarily in a somewhat different aspect 
of the subject, viz., in the aggregate effect of the varied and com- 
plex metabolic processes in reducing, maintaining or increasing 
the stock of matter and of chemical energy in the body. Is the 
body under any given regimen maintaining itself and making 
due growth, or is the animal doing work or yielding milk or 
other products at the expense of its own tissues? This is evi- 
dently a question of balance. Is the income of the body equal 
to its outgo? 

280. The schematic body. — The idea of the organism as 
dependent upon a balance between constructive and destructive 
activities may be made more specific by means of the conception 
of the schematic body, which regards the body of the animal, 
aside from water, as consisting essentially of ash, protein and 
fat, together with an amount of glycogen so small that it may for 
many purposes be neglected. 

The justification for this conception is found in the data con- 
tained in Chapter II, § 3, regarding the composition of the animal 
as a whole. It will be recalled that in the investigations there 
recorded the water, ash and fat were determined directly, the 
difference between the sum of these and the total weight of the 
animal, of course, showing the amount of fat- and ash-free dry 
matter. In those cases in which the total nitrogen contained 
in the body was also determined, it appeared (99) that, with 
one exception, the percentage of nitrogen in this fat- and ash-free 
dry matter closely approximated that in the animal proteins. 
In other words, the amount of glycogen and other substances 
included in the fat- and ash-free dry matter is so small as to be 
negligible and the latter may be considered to consist essen- 
tially of protein. 

From this point of view, it is evident that the effect of any 
feeding stuff or ration in causing a gain or preventing a loss of 
ash, protein and fat (and glycogen) shows its aggregate nutri- 
tive effect. Or, since the organic matter of the body may be 



196 NUTRITION OF FARM ANIMALS 

looked upon in the light of stored energy, a still simpler ex- 
pression of the nutritive effect may be obtained by determining 
the effect of the feed upon the store of protein and of chemical 
energy in the body. 1 

Experiments directed to the determination of the gain or loss 
of matter and of energy by the body have been of two general 
kinds, viz., comparative slaughter tests and what are called 
balance experiments. Both have played an important role in 
the study of nutrition. 

281. Live weight as a measure of nutritive effect. — At the 
very outset, however, the question arises whether the simple 
and obvious method of weighing an experimental animal is not 
sufficient to determine the aggregate effect of a ration, without 
the necessity for any elaborate experimental devices. 

The answer to this question depends largely upon the object 
of the experiment. If it be one undertaken to answer a com- 
mercial question, the increase in live weight during a considerable 
period, when determined with the necessary precautions, may 
be entirely adequate as a measure of the results obtained. If, 
for example, the question under investigation is the relative 
profits of two methods of fattening cattle, the gains made by a 
considerable number of animals, together with the judgment of 
the market regarding the quality of the finished animals, will 
substantially determine which method is to be preferred. The 
use of more elaborate experimental methods would not only be 
a needless refinement but might actually interfere with the 
settlement of the economic question involved. So, too, in the 
handling of young stock or in milk production, the general 
appearance and condition of the animals, together with the gain 
in live weight or the yield of milk, furnishes a sufficiently ac- 
curate indication of the practical results obtained, provided a 
sufficient number of individuals be employed. 

If, however, the purpose of the investigation is to study some 
question relating to the fundamental principles of nutrition, 

1 To make the demonstration absolutely complete, of course, it would be neces- 
sary to show that the stock of each different kind of protein in the body had been 
maintained and that all the energy containing material derived from the feed was 
actually capable of yielding up its energy to the organism. Usually, however, 
especially on a mixed diet, it may be assumed that if the body maintains its stock of 
protein, each particular kind is practically maintained, while no considerable storage 
of unavailable energy in the body has been recognized. 



THE BALANCE OF NUTRITION 



197 



such, for example, as the relative values of the carbohydrates 
and fats, the changes of live weight are of little value as indica- 
tors. For this there are two principal reasons. 

282. Fluctuations in live weight. — In the first place the 
live weight of an animal fluctuates considerably from day to day, 
even when taken under what seem to be identical conditions, 
chiefly on account of variations in the weight of the contents 
of the digestive tract. This is true of all animals, but especially 
of herbivora on account of their comparatively bulky feed, and 
reaches the extreme in ruminants. 



For example, a steer which had been receiving daily for two 
months a uniform ration of 6.35 Kgs. of timothy hay and which was 
kept under as uniform conditions as possible was weighed daily 24 
hours after watering. On February 19 he weighed 419.0 Kgs. and 
on March 6 practically the same amount, 418.6 Kgs. The inter- 
mediate weights, however, were as follows: — 



February 19 
February 20 
February 21 
February 22 
February 23 
February 24 
February 25 
February 26 
February 27 
February 28 
March 1 
March 2 
March 3 
March 4 
March 5 
March 6 



419.0 Kgs. 
431.6 Kgs. 
431.0 Kgs. 
440.6 Kgs. 
431.2 Kgs. 

444.8 Kgs. 
427.6 Kgs. 

427.9 Kgs. 
437.8 Kgs. 
436.0 Kgs. 
437.2 Kgs. 
443.0 Kgs. 
428.4 Kgs. 
433.4 Kgs. 
436.8 Kgs. 
418.6 Kgs. 



It is evident that conclusions based upon a comparison of single 
weighings would have been entirely untrustworthy. Thus a com- 
parison of the live weight of February 19 with that of March 6 would 
have led to the conclusion that the animal was being practically main- 
tained. If, however, the initial weight had chanced to be taken on 
February 20, a comparison with that of March 6 would have shown 
a loss of 13 Kgs., while on the other hand, a comparison of February 
19 with March 5 would have shown a gain of 17.8 Kgs. Even aver- 



198 NUTRITION OF FARM ANIMALS 

aging two or three successive daily weighings, as is often done, while 
it reduces the error does not eliminate it. For example, a comparison 
of the average of February 19-21 with that of March 3-5 shows a 
gain of 8.7 Kgs., while if each average be taken a day later, viz., 
February 20-22 and March 4-6, the comparison shows a loss of 4.8 
Kgs. By increasing the number of single weighings averaged, the 
uncertainty may, of course, be further reduced but not entirely elimi- 
nated, even ten-day averages varying materially, as is illustrated 
by the following figures. 

February 24-March 5, inclusive, 435.3 Kgs. 
February 25-March 6, inclusive, 432.7 Kgs. 
February 26-March 7, inclusive, 432.6 Kgs. 
February 27-March 8, inclusive, 434.2 Kgs. 

A similar reduction of the error may be obtained by the use of a 
number of animals combined into a group which is treated as an in- 
dividual, the fluctuations in the single animals tending to balance 
each other. 

These fluctuations are such as to preclude the use of the 
gain in live weight as a measure of the nutritive effect in exact 
scientific investigations, while it is evident that they must also 
be considered in the planning and interpreting of commercial 
experiments, as well as in judging the effects of rations in prac- 
tice. Such experiments should extend over a considerable 
length of time and include a considerable number of animals, 
while the weights on which comparisons are based should be the 
average of as many single weighings as possible. 

283. Composition of increase. — In the second place, even 
were it possible to ascertain the gain or loss in weight by the 
body tissues proper, exclusive of the contents of the digestive 
tract, i.e., the empty weight, the composition of the material 
gained would still be unknown. An increase of a kilogram in 
tissue weight, for example, might consist chiefly of adipose tissue 
containing 10 or 12 per cent of water (95), or it might be largely 
muscular tissue with 75 or 80 per cent of water (87). Moreover, 
aside from the difference in water content, the dry matter 
of adipose tissue carries more chemical energy than that of 
muscular tissue, so that a gain of a kilogram in the former 
case would be equivalent to the storage of seven or eight times 
as much energy as in the latter. Finally, a knowledge of the 



THE BALANCE OF NUTRITION 199 

kind of material gained or lost is necessary. In the study 
of growth, for example, it is important to know how much of 
the increase in weight is due to a storage of protein, ash, etc., 
i.e., to real growth, and how much to a mere storage of fat or 
water, or both. 

For all these reasons the increase or decrease in live weight, 
while not valueless, is by itself an entirely inadequate measure 
of nutritive effect in investigations into the principles of nu- 
trition. In such experiments it is essential to determine at 
least the gain or loss of the great groups of substances of which 
the body is composed, viz., water, ash, protein, fat and if pos- 
sible carbohydrates, by one of the two general methods already 
mentioned as available for this purpose, viz., the, comparative 
slaughter test or the balance experiment. 

284. The comparative slaughter test. — This method seeks 
to determine by analysis the actual weights of water, protein, 
fat, etc., or the quantities of chemical energy, contained in the 
body of the experimental animal at the beginning and at the 
end of the experiment. Since, however, it is obviously im- 
possible to analyze the same animal twice, its original stock of 
protein, etc., is ascertained by the use of a check animal as 
exactly like the other in age, weight, condition, conformation, 
etc., as it is possible to select, which is slaughtered and analyzed 
at the beginning of the experiment. Assuming initial identity of 
percentage composition for the two animals, the results of this 
analysis are used to compute the weights of the several ingredi- 
ents contained in the body of the experimental animal at the 
outset of the experiment, while the animal itself is analyzed at 
its close. 

The method of comparative slaughter tests has the advantage of 
being a direct determination of the amounts of each ingredient gained 
and of requiring comparatively simple appliances. Furthermore, it 
may be applied not only to the conventional groups of protein, fat, 
etc., but to any substance capable of accurate analytical determina- 
tion. Finally, in addition to the total amount of any substance, its 
distribution between different parts of the body may be ascertained. 
On the other hand, the method has certain drawbacks. 

In the first place, it requires relatively long experimental periods. 
Assuming the work of weighing, sampling and analysis to be correctly 
performed, the accuracy of the results evidently depends upon the 



200 NUTRITION OF FARM ANIMALS 

care and skill exercised in the choice of the check animal. The as- 
sumed identity of composition of the two animals cannot in the nature 
of things be proved and is very unlikely to be absolute. In a short 
experiment, therefore, the error thus possibly introduced may be rela- 
tively large. Its importance diminishes the greater the increase 
made over the original weight, i.e., the longer the period covered 
by the experiment. Furthermore, an experiment by this method 
can be divided into periods only by the use of additional check 
animals, involving additional assumptions as to identity of compo- 
sition at different times, while even these subdivisions, for the reason 
just stated, must be fairly long. Finally, the method is labori- 
ous, especially with the larger animals. The different parts of the 
carcass must be separated, the weight of each part accurately deter- 
mined, avoiding mechanical losses and making due allowance for 
evaporation of water. A correct sample of each part must be 
taken promptly and at once so treated as to preclude any changes 
previous to its analysis. The task of analyzing the carcass of a 
hog or sheep, and still more that of a steer, with the degree of 
accuracy required in a scientific investigation is not one to be un- 
dertaken lightly. 

285. The balance experiment. — The comparative slaughter 
test attempts to determine the weights of the several ingredients 
contained in the body at two different times. The balance 
experiment, on the contrary, consists of a comparison of in- 
come and outgo and does not attempt to determine the original 
stock in the body. If I know that I have a balance of $50 in 
bank at the beginning of the month and $150 at the end, it is 
clear that I have gained $100 in the meantime. This is the 
principle of the comparative slaughter test. On the other hand, 
if I know that my deposits during the month were $500 and my 
drafts $400, I am equally sure that I have gained $100, even 
if I do not know whether my balance at the beginning was $50 
or $500. This is the principle of the balance experiment. If, 
for example, a steer digests 750 grams of protein out of his daily 
ration and if the amount of nitrogenous products excreted in 
24 hours shows that he has katabolized 500 grams of protein, it 
is evident that his original stock of protein, whatever its amount 
may have been, has been increased by 250 grams. By compari- 
sons based on the same general principle, although more com- 
plicated as to details, the increase or decrease of the body's 
stock of fat, glycogen, ash and water or of chemical energy may 



THE BALANCE OF NUTRITION 201 

be determined. The specific methods used for such comparisons 
are described in the two following sections. 

A great advantage of the balance experiment is the comparatively 
short time which it requires. A period sufficiently long for the deter- 
mination of the digestibility of a ration (159) is in general suffi- 
cient also for a balance experiment, while for the requisite determina- 
tion of the respiratory products or of the heat produced twenty-four 
to forty-eight hours suffice, and even this short period may be divided 
into a number of subperiods of a few hours each. For this reason, 
and also because the animal is not injured in the process, repeated 
experiments may be made on the same subject, so that the effect of 
various rations or conditions may be compared on the same individual, 
while the method of comparative slaughter tests necessarily involves 
comparisons between two different animals. 

On the other hand, the complete balance experiment requires elab- 
orate and expensive apparatus, while opinions as to the relative 
amount of labor involved in the two classes of experiments would 
perhaps depend largely upon the previous experience of the experi- 
menter. Furthermore, the balance experiment shows only the amounts 
of the constituent groups — protein, fat, etc. — gained or lost. It 
affords no opportunity to subdivide these and determine the fate of 
single chemical compounds nor does it give any clue to the particular 
region of the body where the gains have been deposited. 

286. The balance of nutrition. — The phrase " balance of nu- 
trition " used as the title of this chapter refers in a general way to 
the balance between income and outgo of matter and energy in the 
body as determined by the methods of the balance experiment. 

Logically, of course, the comparative slaughter test, if com- 
bined with determinations of the feed consumed, may also be. 
regarded as a balance experiment. In it the income of the body 
and the resulting gain are determined, leaving the outgo to be 
inferred, while in a balance experiment in the technical sense, 
the income and outgo are determined and the gain is inferred. 
Nevertheless, the latter type of experiment has played so large 
a part in the study of the balance of nutrition, both for physio- 
logical and for agricultural purposes, that a clear conception of 
its methods and postulates is essential for a comprehension of 
many of the results to be considered in subsequent chapters. 
The subject may be conveniently considered under the two 
heads of the balance -of matter and the balance of energy. 



202 NUTRITION OF FARM ANIMALS 

§ 3. The Balance of Matter 
The gain or loss of protein 

287. The nitrogen balance. — Feed protein which fails to 
be stored up in the body is not excreted as protein but in the 
form of the various products of its katabolism. The gain or 
loss of protein, therefore, cannot be determined by a direct 
comparison of its income and outgo because there is no outgo 
of protein as such. Since, however, the protein of the schematic 
body (280) is equivalent to total nitrogenous matter, the gain or 
loss of protein may be inferred from that of its characteristic 
element, nitrogen, and this is readily ascertained by a com- 
parison of the total nitrogen of the feed with the total nitrogen 
of the excreta, i.e., by a determination of the nitrogen balance.. 

288. Free nitrogen not excreted. — In Chapter V (228) it 
was stated that all the nitrogen of the protein katabolized is 
found in the urea and other organic compounds which are ex- 
creted in the urine. Obviously this is a point of fundamental 
importance. If nitrogen leaves the body only as combined 
nitrogen in the urine and in the feed residues and nitrogenous 
excretory products found in the feces, it is a comparatively 
simple matter to compare the income and outgo. If, however, 
the metabolic processes or the fermentations of the feed in 
the digestive tract yield also gaseous nitrogen, then the nitrogen 
of the respiratory products must also be determined, a task of 
no small difficulty. 

The question of the excretion of gaseous nitrogen has been 
the subject of a vast amount of investigation and controversy. 
Substantially two general methods of experimentation have been 
followed, viz., a comparison of the income and outgo of com- 
bined nitrogen and direct investigation of the respiratory 
products, and the results of both have been in substantial 
accord. The cumulative force of the great number of experi- 
ments in which substantial equality between income and 
outgo of combined nitrogen has been observed under condi- 
tions which precluded the possibility of any considerable gain or 
loss of body protein, together with the fact that the very careful 
and accurate investigations of recent years upon the respiratory 
excretion of free nitrogen have given negative results, amount to 



THE BALANCE OF NUTRITION 



203 



a demonstration that nitrogen leaves the body only in the 
combined form in the visible excreta. 

289. Determination of nitrogen balance. — There being no 
excretion of gaseous nitrogen, a determination of the nitrogen 
balance requires simply a determination of the amounts of this 
element contained in the feed and in the visible excreta. Evi- 
dently this end is already partially attained in a digestion ex- 
periment (158). It is only necessary in addition to provide 
for the quantitative collection and analysis of the urine and, in 
very accurate experiments, of the perspiration and of the epi- 
dermal excreta, in order to obtain data for a comparison of the 
income and outgo of nitrogen, and the same precautions as to 
length of period, uniformity of feeding, etc., which are necessary 
in a digestion experiment, suffice also to render the results of a 
balance experiment representative. 

290. Example of a nitrogen balance experiment. — The digestion 
experiment with clover hay used as an example in Chapter III (160) 
may serve also to illustrate the nature of a nitrogen balance experi- 
ment. In that experiment the hay consumed daily contained 3.144 
Kgs. of dry matter and the daily feces 1.267 Kgs., while the average 
daily weight of the urine for 9 days was 5.449 Kgs. Analysis showed 
the following percentages of nitrogen : — 

In dry matter of hay 2.271 % 

In dry matter of feces 2.240% 

In fresh urine 1.074% 

The brushings of the steer (hair, dandruff, etc.) were found to con- 
tain 1.87 grams of nitrogen per day. The daily nitrogen balance 
may accordingly be computed as follows, showing a loss from the body 
which, of course, must be placed in the income column to complete the 
balance. 

Table 22. — Example of a Nitrogen Balance 



Nitrogen in hay . . . 
Nitrogen in feces . . 
Nitrogen in urine . . 
Nitrogen in brushings . 
Nitrogen lost from body 




Otttgo 
Grms. 



28.40 

58.50 

1.87 

88.77 



204 NUTRITION OF FARM ANIMALS 

291. Computation of protein. — The conception of the sche- 
matic body (280) upon which balance experiments are based 
regards the total nitrogenous matter of the animal as consisting 
substantially of protein. All the vast number of other substances 
containing this element which have been identified as constituents 
of the body are insignificant in amount as compared with the 
great mass of protein which it contains. Accordingly, a gain 
or loss of nitrogen is interpreted as signifying a gain or loss of 
protein and the amount of the latter may be computed from 
the former just as the protein of a feeding stuff is computed from 
its protein nitrogen, it being only necessary to fix upon a suitable 
factor or factors, i. e., to know the average percentage of nitrogen 
in body protein. 

From the results of analyses of entire bodies of animals cited in 
Chapter II, the average nitrogen content of the fat- and ash-free dry 
matter was computed (99) to be : — 

In Lawes and Gilbert's experiments . . . . 16.11% 
In Chaniewski's experiments 16.06 % 

It is probable that in both cases the supposedly fat-free matter 
still contained some fat, it having been subsequently shown that 
extraction with ether does not remove the last traces of it from ani- 
mal tissues. 

Kohler's analyses (88) of the fat- and ash-free lean meat of vari- 
ous species, after correction for the glycogen content of the horse flesh, 
show an average nitrogen content of 16.64 per cent. Since the material 
of Lawes and Gilbert's and of Chaniewski's experiments doubtless in- 
cluded some residual fat and other non-nitrogenous substance, and 
since the larger share of the protein of the body is contained in the 
muscular tissues, it appears justifiable to regard Kohler's figures as 
representing with substantial accuracy the average elementary com- 
position of body protein as a whole, especially since they are the results 
of direct analysis while the others are derived from slaughter experi- 
ments in which the limits of error are somewhat wide. 

Assuming, on the basis of Kohler's results, that average body 
protein contains 16.64 P er cent of nitrogen, the corresponding 
protein factor is 6.0, and the gain or loss of nitrogen observed in 
a nitrogen balance experiment multiplied by this factor gives the 
gain or loss of protein. This is, of course, an approximation, 
since protein is not the only nitrogenous substance contained 



THE BALANCE OF NUTRITION 205 

in the body and since not all the animal proteins contain 
exactly 16.67 P er cent of nitrogen, but the error involved is 
insignificant in most cases so far as it relates to the question of 
the balance between income and outgo. 

On this basis, the steer in the foregoing example was losing 
daily 17.37 X 6.0 = 104.22 grams of body protein. Evidently 
the results of an experiment in which a gain of nitrogen occurs 
can be computed in precisely the same way. 

The gain or loss of fat and glycogen 

292. The carbon balance. — By a method quite similar in 
principle to that just described for protein, it is possible to com- 
pute approximately the gain or loss of body fat from the com- 
bined income and outgo of nitrogen and carbon, while if the 
balance of hydrogen and of oxygen can also be determined the 
computation may be made considerably more exact and may 
include glycogen also. The experimental methods, however, 
are necessarily much more elaborate than those required for a 
simple determination of the nitrogen balance, since it is evident 
that, in addition to the carbon of the feed and of the visible 
excreta, it is necessary to determine the amount of this element 
contained in the gaseous excreta, viz., carbon dioxid and 
methane, while if the balance of hydrogen and oxygen is to be 
included, the hydrogen of the feed, the water excreted and the 
amount of oxygen taken up from the air must also be ascertained. 
An outline of the experimental methods employed for these 
purposes is given in a succeeding paragraph (297), but at the 
outset it seems desirable to confine attention to the principles 
involved. 

293. Computation of gain or loss of fat. -*- According to the 
conception of the schematic body (280) on which the whole 
scheme of the balance experiment is based, substantially all the 
carbon of the body is regarded as existing in the two forms of 
protein and fat. Evidently if a comparison of the income and 
outgo of carbon shows a gain of that element it can, according 
to the fundamental assumption, have been only in one or the 
other or both of these two forms. The nitrogen balance, how- 
ever, shows the amount of protein gained and the carbon con- 
tent of protein is known. If the carbon of the protein gained 



206 



NUTRITION OF FARM ANIMALS 



be subtracted from the total gain of carbon, the remainder 
can have been gained only in the form of fat and the corre- 
sponding amount of this substance can be readily computed. 

294. Example of a carbon balance. — In a respiration experi- 
ment on a steer a complete statement of the nitrogen and carbon 
balances is as follows : — 

Table 23. — Nitrogen and Carbon Balances of a Steer 



6988 grms. timothy hay . 

400 grms. linseed meal . 

16619 grms. feces . . . 

4357 grms. urine . . . 

37 grms. brushings 
4730 grms. carbon dioxid 
142 grms. methan . . 
Gain by body .... 



Nitrogen 



Income 
Grms. 



56.4 
21.9 



78.3 



Outgo 
Grms. 



33-5 

32.4 

i-3 



11. 1 



78.3 



Carbon 



Income 
Grms. 



2831.7 
172.6 



3004.3 



Outgo 
Grms. 



1428.7 

124.2 

8.0 

1290.2 

106.6 

46.6 



3004.3 



The nitrogen balance shows that the animal gained 11.1 X 6.0 = 
66.6 grams of protein. According to Kohler's results (88), the 
average protein of cattle contains 52.54 per cent of carbon. Conse- 
quently, the protein gained in this experiment contained 66.6 X .5254 
= 35.0 grams of carbon. The total gain of carbon, however, as 
shown by the carbon balance, was more than this, viz., 46.6 grams, and 
we accordingly have the following : — 



Total gain of carbon . . 
Carbon in protein gained 

Carbon gained as fat 



46.6 grams 
35-Q grams 
1 1.6 grams 



The elementary composition of animal fat was shown in Chapter 
I (34) to be very uniform, averaging 76.5 per cent of carbon. A 
gain of 0.765 gram of carbon in the form of fat, therefore, is equiva- 
lent to a gain of one gram of fat or a gain of one gram of carbon to 
1. 3 1 grams of fat, and accordingly the gain of 11.6 grams of carbon 
in the form of fat shows a gain by the animal of 11.6 -£■ 0.765, or 
11. 6 X 1. 31 = 15.2 grams of fat. Substantially the same method of 



THE BALANCE OF NUTRITION 207 

computation can, of course, be applied when there is a loss of nitro- 
gen or carbon or both. 1 

295. Gain or loss of glycogen. — The only non-nitrogenous organic 
substance other than fat present in the body in sufficient amounts to 
affect the foregoing computations is glycogen. It is generally assumed 
that under reasonably normal conditions of feeding the glycogen con- 
tent of the body does not fluctuate materially, so that any consider- 
able or long continued gain of carbon, other than that contained in 
protein, is in the form of fat. Probably this is not equally true in 
the case of a loss of carbon, and in any case the results of computations 
like that of the preceding paragraph are evidently subject to a degree 
of uncertainty as regards a possible gain or loss of glycogen by the 
body. While this is probably not serious in reasonably long periods 
it may be relatively important in short experiments. If, however, 
there can be added to the determination of the nitrogen and carbon 
balance that of the balances of hydrogen and oxygen the means are 
afforded for a more accurate calculation, since it is evident that the 
amounts of the latter two elements, especially of oxygen, retained in 
the body would be greater in the case of a storage of glycogen than in 
that of a storage of fat containing the same amount of carbon. The 
method of computation is, however, somewhat complicated and need 
not be gone into here. 2 

296. The respiratory quotient. — The respiratory quotient is 
the ratio of the volume of carbon dioxid excreted by an 
animal to the volume of oxygen taken up during the same time, 

. . . V0I.CO2 « . .„ , • , 

i.e., it is • The respiratory quotient will obviously 

Vol. O2 

vary according to the kind of material which is being katabo- 
lized in the body. Thus in the oxidation of carbohydrates each 
liter of oxygen consumed gives rise to the production of one 
liter of carbon dioxid and the respiratory quotient therefore 
is 1.0. On the other hand, when fat is oxidized, a portion of the 
oxygen unites with the hydrogen of the fat and only the re- 
mainder is available for the production of carbon dioxid. It 
is easy to compute, therefore, that each liter of oxygen con- 
sumed in the oxidation of fat will give rise to the production of 

1 To avoid errors in computation it is convenient to regard losses in such compu- 
tations as negative gains and to carry through the computation exactly as in the 
above experiment, using the algebraic sum or difference in every instance. 

2 See Atwater and Benedict, A Respiration Calorimeter, etc., Carnegie Institu- 
tion of Washington, Publication No. 42 (1905). 



208 NUTRITION OF FARM ANIMALS 

0.7 liter of carbon dioxid. Similarly, it may be computed that 
if protein of average composition be oxidized to urea, carbon 
dioxid and water, the respiratory quotient will be approxi- 
mately 0.8, although in reality the quotient for protein varies 
according to the nature of the nitrogenous products formed and 
the amount of carbon thereby withdrawn from oxidation to 
carbon dioxid. Ordinarily, however, the proportion of the 
gaseous exchange of the body due to the katabolism of protein 
is comparatively small, so that if, for example, the respiratory 
quotient closely approaches 1.0, it is clear that the katabolism 
must be chiefly that of carbohydrates, while if, on the other 
hand, its value approaches 0.7, it is equally evident that the 
katabolism must be chiefly that of fat. Values for the respira- 
tory quotient intermediate between these extremes imply that 
the katabolism is in part that of fats (or proteins) and in part 
that of carbohydrates. 

The respiratory quotient of course affords no information 
regarding the balance between income and outgo but its deter- 
mination gives valuable information as to the nature of the 
material which is being katabolized in the body, particularly 
in short periods. 

297. The respiration apparatus. — A determination of the 
gaseous exchange of an animal, such as is necessary in order to 
formulate the complete balance of matter, requires the use of 
some form of special apparatus known as a respiration apparatus. 

In its simplest and earliest form the respiration apparatus 
consisted of a closed chamber of known capacity, such as was 
used by Crawford, Mayow, Black, Priestly, Lavoisier and 
others in their early experiments. The animal was placed in 
the hermetically sealed apparatus and the changes in the com- 
position of the enclosed air which were brought about by its 
respiration were determined. Evidently, however, the method, 
while charmingly simple, is open to objections. The oxygen 
of the air is gradually consumed, while the carbon dioxid and 
other products of respiration accumulate. Even if the experi- 
ment be broken off before fatal results to the animal ensue, it 
is made under varying and increasingly abnormal conditions, 
while no very long trials are possible. 

Two obvious methods of avoiding this difficulty at once 
suggest themselves; either to absorb the products of respira- 



THE BALANCE OF NUTRITION 



209 



tion and replace the oxygen consumed or to conduct a current 
of air through the apparatus. Correspondingly, two different 
types of respiration apparatus have been evolved, known re- 
spectively as the closed circuit and open circuit apparatus, 
or from the names of the investigators who first developed them 
into practicable appliances, as the Regnault-Reiset and the 
Pettenkofer apparatus. Each of these two types may be sub- 
divided into those intended to determine the total gaseous ex- 
change of an animal and those which take account only of the 
pulmonary exchange. . 

298. The Regnault-Reiset apparatus. — In the closed cir- 
cuit, or Regnault-Reiset apparatus, respiration takes place in 



RESPIRATION 
used 



CHAMBER 



M,0 N 



^produced 



&, deficient 



^ 



1 o introduced 



deficient ■ 



CO- 

ab&orbed 014 



U 



/Na OH \ 

"1 \Ca[OHl,) J I 



HjO 

absorbed bu. 

h.scu 



ROTARY 
BLOWER 



Fig 24 — Scheme of closed circuit respiration apparatus. (Atwater and Benedict, 
Carnegie Institution of Washington, Publication No. 42.) 

a confined volume of air, the possibility of any exchange be- 
tween it and the outside atmosphere being carefully guarded 
against. By suitable mechanical means (a blower, for instance) 
the confined air is kept in circulation over suitable absorbents 
which take up the water and carbon dioxid given off, while 
the oxygen consumed is replaced from a gasometer or a cylinder 
of the compressed gas. The general scheme for such an ap- 
paratus is shown in Fig. 24. The increase in weight of the ab- 
sorbents plus any increase in the amount of carbon dioxid and 



2IO 



NUTRITION OF FARM ANIMALS 



water contained in the air of the apparatus shows the amounts 
of these substances produced, while the amount of fresh oxygen 
admitted minus any increase of the oxygen contained in the air 
of the apparatus shows the quantity of this element absorbed. 




Any methane or hydrogen excreted accumulates in the ap- 
paratus and may be determined by an analysis of the contained 
air at the close of the experiment. The amount of nitrogen 
contained in the apparatus should, of course, remain unchanged 
if the apparatus is working properly. . 



THE BALANCE OF NUTRITION 



211 




o 

> 



:3 

J3 



c 






3 

G 
CuO 

o 

P4 



O 
fa 



212 NUTRITION OF FARM ANIMALS 

If the entire respiratory exchange is to be determined, the 
subject is placed in the respiration chamber represented in the 
diagram. If only the pulmonary exchange is under investi- 
gation, the respiration chamber is replaced by a mask or mouth- 
piece or even by a suitable cannula inserted in the trachea. 

The original form of the Regnault-Reiset apparatus 1 is shown in 
Fig. 25. The same investigators subsequently devised a larger one 
in which they made a number of experiments upon animals of various 
species including sheep, calves, swine and fowls. In theory this is 
the most perfect form of respiration apparatus, but numerous tech- 
nical difficulties arise in its use. Various later forms have been de- 
vised but Atwater and Benedict 2 were the first to construct one of a 
size suitable for man which was capable of a high degree of accuracy. 
Quite recently Zuntz 3 has constructed a respiration apparatus of 
this type for experiments on domestic animals, a section of which 
is shown in Fig. 26, while for the determination of the pulmonary 
exchange, Benedict 4 has devised a so-called "Universal" respiration 
apparatus. 

299. The Pettenkofer apparatus. — In the Pettenkofer, or 
open circuit, respiration apparatus, the subject breathes in a 
continuous measured current of atmospheric air whose content 
of water, carbon dioxid and methane is determined before and 
after passing the animal, the difference, of course, showing how 
much of each gas the subject has added. In an apparatus suit- 
able for small animals the entire amount of carbon dioxid and 
water in the incoming and outgoing air current may be deter- 
mined, but in the larger forms it is necessary to measure the air 
current and make analyses upon relatively small samples, so that 
the analytical errors are multiplied by a large factor, while a de- 
termination of the oxygen balance has not as yet been found 
practicable. The general scheme of such an apparatus is shown 
in the diagram, Fig. 27. As in the case of the Regnault-Reiset 
apparatus, the respiration chamber may be replaced by a mask, 
mouthpiece or cannula for the investigation of the pulmonary 
exchange. 

1 Ann. de Chem. et de Physique, 3« me Series, 26, 299. 

2 Carnegie Institution of Washington, Publication No. 42 (1905). 

3 Landw. Jahrb., 44 (1913), 776. 
4 Deut. Arch. Klin. Med., 107 (191 2), 156. 



THE BALANCE OF NUTRITION 



213 



The first practicable form of open circuit apparatus was devised 
by Pettenkofer 1 for experiments on man. Its general appearance is 
shown in Fig. 28. The comparative simplicity of its operation and 



» > 



METER. 



RESPIRATION CHAMBER 



CO z { PRODUCED 



£ 



METEP. 



9 > 




J— ME1 



METER 



N z O<5CO z CH+ J^OSCO^ 

ABSORBED OXIDJZED ABSORBED 
Fig. 27. — Scheme of Pettenkofer respiration apparatus. 

the fact that it could be readily built of any desired size led to its 
extensive use in investigations upon agricultural animals, notably by 
Henneberg and Stohmann at Gottingen, Stohmann at Leipzig and 
G. Kiihn and later Kellner at Mockern. 




Fig. 28. — Pettenkofer respiration apparatus. 
Explanatory sketch. (Atwater, U. S. Department of Agriculture, Office of Experiment 
Stations, Bulletin No. 21.) 



1 Ann. Chem. Pharm., Suppl. Bd. II, p. 1. 



214 



NUTRITION OF FARM ANIMALS 



The principle of the Pettenkofer apparatus has also been very 
extensively used for the investigation of the pulmonary exchange, 
especially by Zuntz and his associates, to whom the development of 
this form is largely due. Figure 30 shows a horse equipped with a 
tracheal cannula for experiments with this type of apparatus. Ow- 
ing to the fact that the excretory gases are not diluted with many 
times their volume of air, as is the case when a respiration chamber is 
used, the results are much sharper and it is possible to determine 
the amount of oxygen consumed as well as that of carbon dioxid 
given off. 




Fig. 29. — The Mockern respiration apparatus. (Bailey's Cyclopedia of Ameri- 
can Agriculture.) 

300. Investigation of pulmonary exchange. — For many pur- 
poses a determination of the gaseous exchange in the lungs, 
either with the Regnault-Reiset or the Pettenkofer type of 
apparatus, is preferable to determinations of the total exchange 
in a respiration chamber. The former method is especially 
adapted for short experiments. By its use, it is possible to 
trace sharply changes in the amount of the metabolism, the 
respiratory quotient, etc., produced by the administration of 
feed substances, drugs, etc., by experimental lesions, and es- 
pecially by work, — changes whose amounts would often be 
relatively very small as compared with the total excretion for 
24 hours as measured in the respiration chamber and which, 
therefore, if they did not escape detection altogether, could not 
be as accurately determined either quantitatively or chrono- 
logically. On the other hand, it is impracticable to continue 
its use through long periods, — a day, e.g., — and since it takes 



THE BALANCE OF NUTRITION 



215 




2l6 NUTRITION OF FARM ANIMALS 

no account of the excretion through the skin and the alimentary 
canal, it is only by indirect methods that it is possible to com- 
pute the total balance of carbon, hydrogen and oxygen by its 
use. 

301. Balance of water and of ash ingredients. — The res- 
piration apparatus of either type serves to determine the ex- 
cretion of water vapor by the subject as well as that of carbon 
dioxid and other gases and thus, in connection with the neces- 
sary analyses of the feed and visible excreta, to establish the 
gain or loss of hydrogen. Unfortunately, more or less difficulty 
is experienced in determining accurately the hydrogen balance 
owing in part to the liability to condensation of water in the 
apparatus and in part to the fact that the amount of organic 
hydrogen actually entering into the metabolism of the animal 
is small as compared with the amounts of water consumed and 
simply evaporated again. 

The ash ingredients, of course, with the possible exception 
of minute amounts of sulphur, all leave the animal in the visible 
excreta and the balance of these elements may therefore be 
determined according to the same principles as the balance of 
nitrogen. 

§ 4. The Balance of Energy 

302. Balance of nutrition includes energy. — Since the 
animal body is essentially a transformer of energy (207), the 
balance of nutrition is not only concerned with the income and 
outgo of matter but also, corresponding to the dual function of 
feed (263), with the gain or loss of energy by the body. The 
study of the balance of energy is a method of investigating 
some of the important problems of nutrition which has been 
especially developed in recent years and which has proved 
fruitful of results. Before entering upon its consideration, 
however, a brief review of some of the elementary concepts of 
energetics as related to physiological processes may not prove 
superfluous. 

Elementary principles 

303. Energy. — Up to this point the word energy has been 
used without any precise definition. In a specific study of the 



THE BALANCE OF NUTRITION 217 

balance of energy, however, it is important to have as definite 
a conception as possible of what is meant by the term. It is 
not altogether easy to give a simple general definition of energy, 
but for the present purpose that given by Noyes * may be 
adopted, viz., " That which gives rise to changes in the prop- 
erties of bodies and to the power to produce such changes." 
For the present purpose, however, the conception of energy may 
be more readily apprehended from illustrations than from defi- 
nitions. 

The subject may be conveniently approached from the side 
of mechanics. A moving body is capable of producing certain 
effects by virtue of its motion. The falling weight of a pile 
driver, for example, forces the pile downward against the re- 
sistance of the ground and at the same time produces heat at 
the point of impact. The projectile fired from a sixteen inch 
gun striking the side of the armored ship overcomes the cohesive 
force of the armor plate and deforms or penetrates it, while 
the blow also gives rise to an evolution of heat. The blows of 
the blacksmith, if rapid and heavy enough, may raise the iron 
on his anvil to a red heat. Accordingly, it is said that a moving 
body possesses energy in the form called kinetic energy, or energy 
of motion. 

If a body suspended above the earth is set free it falls to the 
ground, and at the moment of contact with the earth possesses 
a certain amount of kinetic energy which was generated during 
its fall from something which was not energy of motion. This 
other form of energy, which the body possessed previous to 
its fall by virtue of its position, may be called gravitation energy. 
The same relation is illustrated by a swinging pendulum. Dur- 
ing the downward swing, the gravitation energy which it pos- 
sessed when at its highest point is converted into kinetic energy, 
while when it rises the kinetic energy which it possesses is re- 
converted into gravitation energy. When we lift a weight we are 
conscious of expending work, which is stored up as gravitation 
energy, to be liberated again as kinetic energy when the weight 
falls. 

304. Forms of energy. — In general, whenever the rate of 
motion of a body is increased (or, to use a more familiar if less 
accurate expression, whenever motion is produced) it is to be 

1 General Principles of Physical Science, 1902. 



2l8 NUTRITION OF FARM ANIMALS 

inferred, as in the case of the falling body or the pendulum, that 
the kinetic energy produced has been derived from some other 
form of energy. In the examples thus far given this other form 
of energy was gravitation energy. In many familiar instances, 
however, this is not the case. The expanding steam in the 
cylinder of a steam engine parts with some of its heat to produce 
the motion of the piston. The electric current in the wire sets 
the armature of the motor in revolution. The combustion of 
gasoline in the cylinder of an engine produces motion of the 
engine as well as heat. Heat, electricity and chemical action 
may all be sources of kinetic energy and therefore the existence 
of heat energy, electrical energy and chemical energy is inferred. 
The manifestations of energy are of the most varied charac- 
ter but its forms may be conveniently grouped under the fol- 
lowing general heads : — 

i. Kinetic energy 6. Magnetic energy 

2. Gravitation energy 7. Chemical energy 

3. Cohesion energy 8. Heat energy 

4. Volume energy 9. Radiant energy 

5. Electrical energy 

Of these, kinetic energy, chemical energy and heat energy 
are those of most importance in considering the balance of en- 
ergy in the animal body. 

305. Transformations of energy. — As is illustrated by the 
examples given in the previous paragraphs, and as has been 
assumed in speaking of energy changes in the animal body, the 
various forms of energy are capable of mutual transformations. 
Heat may be converted into motion in the heat engine. Motion 
in turn is converted into heat when a moving body is retarded 
by friction or stopped by contact with another body. When 
gasoline is burned freely, its chemical energy is converted into 
heat, but when it is exploded in the cylinder of an engine it 
yields also motion. This motion in turn may be stored in the 
form of gravitation energy in a lifted weight, or as cohesion 
energy in a coiled spring, or it may be made a source of elec- 
trical energy which in its turn gives rise to the radiant energy 
of light in the filament of a lamp. 

In brief, all the physical phenomena of the universe of which 
we can take cognizance can be described in terms of changes of 



THE BALANCE OF NUTRITION 219 

energy either as to form or intensity, and this fact has led some 
physicists to identify the concepts, of matter and energy and to 
maintain that the former can be fully interpreted in terms of 
the latter. Without entering here into this debated question, 
it will be convenient to follow for our present purpose the more 
familiar course of regarding matter and energy as two distinct 
although indissolubly connected entities. 

306. The conservation of energy. — When a unit of kinetic 
energy is converted into heat energy it is found that the amount 
of heat obtained is- always the same no matter what the process 
employed in effecting the conversion. Similarly, if a unit of 
heat be converted into kinetic energy the amount of the latter 
obtained is always the same and moreover is always equal to 
the quantity of kinetic energy which disappears when one unit 
of heat is produced. 

What is true of heat energy and kinetic energy in this respect 
has been shown to be true of all the forms of energy. Not only 
are they convertible into each other but there is no loss or gain 
of energy in the conversion. When a quantity of energy of one 
form disappears an equivalent quantity simultaneously appears 
somewhere in some other form or forms. This great generali- 
zation, perhaps the most important in the history of physical 
science, is known as the law of the conservation of energy, or 
the first law of energetics. It was first clearly and distinctly 
formulated by Mayer in 1842 and since that time has been 
verified by a great number of the most exact experiments and 
forms the basis of modern conceptions of physical processes. 
In substance, it asserts that the total energy of the universe 
as far as man knows it is a constant quantity, subject to con- 
tinual changes of form but neither created nor destroyed. 

That the law of the conservation of energy applies to the 
processes taking place in the body of the animal was exceedingly 
probable, a priori, and has been demonstrated experimentally 
by the researches of Rubner upon dogs, of Laulanie on various 
animals, of Atwater, Benedict, Lusk and their associates upon 
men and of Armsby and Fries upon cattle. 1 The impor- 
tance of this fact in relation to the study of energy changes in 
the body is obvious. 

1 Compare the writer's Principles of Animal Nutrition, pp. 263-268 and Penna. 
Expt. Sta., Bui. 126. 



2 20 NUTRITION OF FARM ANIMALS 

307. Heat energy unique. — In one respect heat energy 
occupies a peculiar position. Other forms of energy are in 
general readily and completely transformed into heat but there is 
no known method by which heat can be completely transformed 
into other forms, such as kinetic energy. Whatever portion of 
the heat is thus transformed obeys the law of the conservation 
of energy but part of it always remains in the form of heat. 1 

308. Units of energy. — Quantities of energy are measured 
by converting them into the same form and comparing them 
with some quantity of the same form of energy arbitrarily as- 
sumed as a unit. 

Since quantities of kinetic energy can be expressed in terms 
of mass, space and time, a unit based on these concepts is taken 
as the fundamental unit of energy. The so-called C. G. S. 
(centimeter-gram-second) unit is the erg. An erg is a quantity 
of energy equal to twice the kinetic energy possessed by a mass 
of one gram moving with a velocity of one centimeter per second. 
Since this is a very small quantity, a unit called the joule, equal 
to ten million ergs, is often employed in practical measurements 
of energy, that is, i joule = io 7 ergs. For purposes where a still 
larger unit is desired the kilo-joule equal to one thousand joules 
is also employed. 

In practice, however, heat is the form of energy which gen- 
erally lends itself most readily to exact determination and, 
since other forms of energy are easily converted into heat, units 
of heat are extensively employed in the study of energy. The 
most common unit for this purpose is the calorie, which is the 
quantity of heat required to raise the temperature of one gram 
of water one degree centigrade. 2 

The foregoing is known as the small, or gram calorie (cal.). 
Where larger quantities of heat are to be measured the large, 

1 This is, of course, one aspect of the second law of energetics. Theoretically, 
a perfect heat engine with a lower temperature limit of absolute zero would convert 
heat completely into kinetic energy. Since, however, we can neither obtain the 
temperature of absolute zero nor construct a perfect heat engine, this theoretical 
conception is simply a limit which may be more or less remotely approached in 
practice but never attained. 

2 Since the specific heat of water varies at different temperatures, an exact defini- 
tion of the calorie must specify the temperature at which it is measured. Practice 
differs in this respect but the preferable unit is the mean calorie, which is one one- 
hundredth of the amount of heat required to raise the temperature of one gram of 
water from o° to ioo° C. 



THE BALANCE OF NUTRITION 



221 



or kilogram calorie (Cal.), equal to one thousand small calories, 
is employed, while for still larger quantities the Therm, equal 
to one thousand large calories, may be used. In the following 
pages the term calorie signifies the large, or kilogram, calorie, 
unless the contrary is expressly stated. 

Certain units of gravitation energy are also frequently used, 
especially in mechanics, the more important ones being the 
gram meter, the kilogram meter and the foot pound. The 
gram meter is the energy required to raise a weight of one gram 
vertically through one meter in opposition to gravity, the kilo- 
gram meter is the energy required to raise a weight of one kilo- 
gram through one meter, and the foot pound is the energy re- 
quired to raise a weight of one pound through one foot. Since 
the force of gravity varies at different points on the earth's 
surface these units as thus defined are not invariable. Taking the 
average force of gravity at sea level, however, as equal to 980.5 
dynes, the relations between these various units are as follows : 

EQUIVALENCE OF UNITS OF ENERGY 



1 gram meter . . 
1 kilogram meter 
1 foot pound . . 
1 calorie . . . 
1 Calorie . . . 



Ergs 


Gram 
Meters 


Kilogram 
Meters 


Foot 
Pounds 


Gram 
Calo- 
ries 


980.5 X 102 
980.5 X io 5 
135-5 X io 5 
4.184 Xio? 
4.184 X io 1 " 


1000 

138.2 

426.6 

426600 


O.OOI 

0.1382 
0.4266 

426.6 


0.007236 
7.236 

3.087 
3087 


0.002344 

2.344 

0.3239 

1000 



Kilogram 
Calories 



0.2344 X io- 6 

0.002344 

0.000324 

O.OOI 



309. Measurement of heat energy. — Quantities of heat 
are measured chiefly in two ways, viz., by their effects in raising 
the temperature of some substance or in changing its state of 
aggregation. Instruments for measuring quantities of heat 
are called calorimeters, i.e., heat measurers. 

In the first method, as already implied in the definition of the 
calorie (308), water is ordinarily used as the calorimetric sub- 
stance. 1 For example, if the quantity of heat to be measured 
can be transferred without loss to a kilogram of water, and if 
the temperature of the water is thereby raised 2 C, it is evi- 
dent that the quantity of heat imparted to it is two large calo- 

1 Other substances than water may, of course, be employed, but water is usually 
the most convenient. 



222 



NUTRITION OF FARM ANIMALS 



ries. A calorimeter constructed after this principle is a water 
calorimeter. Such calorimeters have been devised in a great 
variety of forms according to the special purpose in view. The 
two essential requirements are that any escape of heat by con- 
duction or radiation shall be either preventable or measurable 
and that the temperature increase be accurately determined. 

In the second method the heat is caused to expend itself in 
changing the physical state of some substance as, for example, 
in melting ice or in evaporating some volatile liquid. The ice 




Fig. 31. — Lavoisier's ice calorimeter. (Schaefer, Text Book of Physiology.) 

calorimeter is one of the oldest forms of calorimeter and has been 
extensively used for certain classes of work. Figure 31 shows a 
simple form of ice calorimeter used by Lavoisier. The source 
of heat is placed in the central vessel and imparts its heat to 
the surrounding ice, while the access of any extraneous heat is 
prevented by the outside jacket of ice. 

In Lavoisier's calorimeter the amount of ice melted was determined 
by collecting and weighing the resulting water, but a much more 
accurate method of measurement is based upon the contraction which 
ice undergoes when converted into water. 



THE BALANCE OF NUTRITION 223 

By means of the water calorimeter, it has been determined 
that the conversion of one gram of ice at o° C. into liquid water 
at the same temperature requires 79.24 gram calories of heat. 
By the use of this factor the indications of the ice calorimeter 
can be converted into calories. 

310. Heats of Combustion. — As related to nutrition in- 
vestigations, the chemical energy of an organic substance is 
most commonly measured by converting it into heat by complete 
combustion with oxygen and measuring the heat by one of the 
methods just indicated, the result being called the heat of com- 
bustion of the substance. In the method most commonly used 
in nutrition investigations, the substance is burned in highly 
compressed oxygen (about 25 atmospheres) in a lined steel 
bomb, the heat being taken up by water. The method was 
first devised by Berthelot and subsequently modified by Mahler, 
Hempel and Atwater. One form of this calorimeter is shown 
in section in Fig. 32. 

311. Heats of combustion do not measure total energy. — 
It should be clearly understood that the heat of combustion of 
an organic compound does not, as is sometimes erroneously 
stated, measure its total energy but simply the amount mani- 
fested in a particular chemical change. Thus, in the complete 
oxidation of one gram of starch to gaseous carbon dioxid and 
liquid water 4183 gram calories of energy are transformed into 
heat. How much additional energy is still contained in the 
resulting carbon dioxid and water we do not know, nor is it 
necessary that we should. In using the heat of combustion as 
a measure of the chemical energy of starch the possible energy 
content of the carbon dioxid and water is simply assumed as 
an arbitrary zero, much as the engineer may assume a datum 
plane for his levels without regard to its height above sea level. 
In other words, the heat of combustion of starch or of any other 
substance shows how much chemical energy can be secured 
from it for conversion into other forms by processes of oxidation 
such as occur in the body. 

312. Law of initial and final states. — In view of the very 
complicated nature of the metabolic processes, the question 
naturally arises whether the amount of chemical energy which 
a feed ingredient such as starch really puts at the disposal of 
the organism is the same as the amount of chemical energy which 



224 



NUTRITION OF FARM ANIMALS 



l..,.„. i:„:i,i.n:, ■■ ,. ■ ■'„; ;"i 




f'iG. 32. — Section of bomb calorimeter. (Atwater, U. S. Department of Agri- 
culture, Office of Experiment Stations, Bulletin No. 21.) 



THE BALANCE OF NUTRITION 225 

is transformed into heat by its almost instantaneous burning 
in oxygen. The answer to this question is found in what is 
called the law of initial and final states. 

This law is that in any independent system the amount of 
energy transformed during a change in the system depends 
solely upon the initial and final states of the system and not 
at all upon the rapidity of the transformation nor upon the kind 
or number of the intermediate stages through which it passes. 
Although this law is true in the general form here stated, it was 
originally propounded as related to chemical reactions. If we 
start with starch and oxygen and end with the corresponding 
quantities of carbon dioxid and water, the amount of chemical 
energy converted into heat or other forms is the same, no matter 
whether the starch be burned almost instantaneously in pure 
oxygen or whether it be subjected to slow oxidation in the tissues 
of a plant buried in the soil ; whether carbon dioxid and water 
are the immediate products of the action or whether the starch 
passes through intermediate stages like maltose, glycogen, 
dextrose, lactic acid, etc., etc., as in the body of the animal. It 
is simply necessary to determine the difference in chemical 
energy between the system in its initial and in its final state 
to obtain the amount of energy transformed during the 
change. 

313. Measurement of kinetic energy. — The most common 
method of measuring the energy liberated by a machine or an 
animal as motion energy is its conversion, actually or virtually, 
into gravitation energy, which is measured by the units given 
on a previous page (308). In case of small amounts of energy 
a weight may be actually lifted, the product of weight into 
distance giving the number of gram centimeters or foot pounds 
of energy expended. In other cases, the subject may pull 
against a resistance produced, for example, by the friction of a 
brake, the traction being measured by some form of spring 
balance. In this case the kinetic energy is, as a matter of fact, 
converted into heat, but the tractive pull multiplied by the 
distance gives the equivalent number of gravitation units. In 
still another form the subject virtually lifts his own weight by 
climbing the inclined plane of a tread power, the body weight 
multiplied by the distance multiplied by the sine of the angle 
of ascent equaling the units of gravitation energy to be measured. 
Q 



226 



NUTRITION OF FARM ANIMALS 



Figure 33 shows a form of this apparatus used by Zuntz for 

work experiments upon horses. 

Another method for measuring kinetic energy consists in 

converting it into electrical energy by causing the subject to 

work against the resistance 
of a magnetic field. The 
amount of current thus gen- 
erated can be measured in 
electrical units, or, as has 
been done by Atwater, Bene- 
dict and others, the electrical 
energy may be converted into 
heat and measured in calories. 




1 



1 




< 



o 



V 



T3 



The body's income of energy. 
— Gross energy 

314. Only chemical energy 
can be utilized. — As was 
stated in the introductory 
paragraphs of this chapter, 
the animal body resembles an 
internal combustion motor in 
being a mechanism for the 
conversion of the chemical 
energy of certain compounds 
contained in the feed into 
kinetic energy. In consider- 
ing the balance between in- 
come and outgo of energy, it 
is essential to recognize a 
further point of resemblance, 
viz., that neither the animal 
nor the motor can utilize 
other than chemical energy. 
There is no evidence that the 
animal body can use in any 
way any of the other forms 
of energy, such as heat, elec- 
tricity or solar radiation 



THE BALANCE OF NUTRITION 227 

which reach it from its environment, any more than the gasoline 
engine can use the energy of falling water or of an electric cur- 
rent. Chemical energy is not merely a source but the only source 
from which the animal body can derive its supply. 

315. Gross energy. — The income of energy may be ascer- 
tained, therefore, by determining the chemical energy con- 
tained in the various compounds present in the feed in the 
manner already indicated (309), viz., by converting it into heat 
and measuring the amount of the latter by means of a suitable 
calorimeter. In other words, the income of chemical energy is 
measured by the heat of combustion of the feed. In order to 
avoid the implication that this is the total amount of energy 
associated with the feed (311), it will be convenient to use the 
term gross energy as equivalent to the amount of energy mani- 
fested as heat when the feed is completely oxidized. 

Since the chemical energy of a feeding stuff is converted into 
heat for purposes of measurement, its amount is usually ex- 
pressed in heat units. It should be clearly understood, however, 
that this is simply a matter of convenience and that it is the 
chemical energy of feeding stuffs and not the heat produced by 
their combustion which is of use to the animal. 

It is scarcely necessary to point out that the gross energy of 
the feed does not measure its nutritive value. Otherwise, 
anthracite coal, with a heat of combustion of some 7.9 Cals. 
per gram, would outrank most feeding stuffs, while hydrogen 
gas, with a heat of combustion of more than 34 Cals. per gram 
would stand still higher in the list. Obviously, the feed value 
of a substance depends not only upon its content of gross energy 
but upon the proportion of the latter which the body can 
utilize. 

316. Heats of combustion. — The heats of combustion of a 
great variety of organic substances have been determined. 
Atwater 1 in 1895 published a compilation of results upon a 
large number of compounds of importance in nutrition, Fries 2 
has prepared a rather more extensive list, and Benedict and 
Osborne 3 have determined the heats of combustion of nineteen 
vegetable proteins. 

1 U. S. Dept. Agr., Office Expt. Stas., Bull. 21 (1895). 

2 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 94 (1907). 

3 Jour. Biol. Chem., 3 (1907), 119. 



228 



NUTRITION OF FARM ANIMALS 



The following tabulation may serve to give a general idea of 
the gross energy of some of the more important substances 
concerned in nutrition. It should be specially noted that the 
figures given are in most instances simply approximate averages. 

Table 24. — Approximate Gross Energy 



Animal protein .... 
Vegetable protein . . . 
Carbohydrates .... 

Sucrose 

Animal fats 

Butter fat 

Vegetable fats .... 
Ether extracts of seeds 
Ether extracts of roughages 



Per Kilo- 
gram 


Per 100 
Pounds 


Cals. 


Therms 


5700 
5636 
4185 


258.6 

255-7 
189.8 


3955 


179.4 


9500 


43Q-9 


9200 


417-3 


9470 

9467 
7962 


429.6 
429.4 
361.2 



The following examples taken from the work of Kellner and of 
Armsby and Fries will serve to give a general idea of the gross 
energy of common feeding stuffs. It will be observed that the 
range of variation is relatively small in most instances. 

Table 25. — Gross Energy of Feeding Stuffs 



Roughage 

Timothy hay . 
Red clover hay 
Mixed hay . . 
Alfalfa hay 
Meadow hay . 
Corn stover 
Oat straw . . 
Wheat straw . 
Straw pulp 



Per Kilo- 
gram 


Per 100 
Pounds 


Cals. 


Therms. 


45i8 
4462 


204.94 
202.04 


4393 
4372 


199.27 
198.31 


4433 
4332 
4436 


201.08 
196.50 
201.22 


4444 
4147 


201.58 
188.11 



THE BALANCE OF NUTRITION 



229 



Concentrates 

Corn meal .... 
Hominy chop . 
Wheat bran . . . 
Grain mixture No. i a 
Grain mixture No. 2 b 
Beet molasses . . 

Starch 

Peanut oil . . . . 
Wheat gluten . . . 



Per Kilo- 
gram 


Per 100 
Pounds 


Cals. 


Therms. 


4442 


201 


49 


4709 


213 


60 


4532 
4685 
4609 

3743 
4152 


205.57 
212.51 
209.06 
169.80 
188.35 


9457 


429 


00 


5579 


253 


10 



a. Wheat bran, 14.28 per cent; corn meal, 42.86 per cent; old process linseed 
meal, 42.86 per cent. 

b. Corn meal, 60 per cent ; crushed oats, 30 per cent ; old process linseed meal, 
10 per cent. 

Some data are also available regarding the gross energy of the 
digested nutrients of feeding stuffs. The following averages are 
derived chiefly from Kellner's investigations. 

Table 26. — Gross Energy of Digested Nutrients 



Protein of wheat gluten . . . 
Protein — assumed average . . 

Crude fiber 

Nitrogen-free extract of hay 
Nitrogen-free extract of starch . 
Ether extract of hay .... 

Peanut oil 

Total organic matter of roughage 




Per 100 
Pounds 



Therms. 
271.O 
258.6 
193.O 
192.O 
189.8 

377-5 
400.I 
202.9 



In the computation of energy balance, the factors commonly 
used are, for body protein 5.7 Cals. per gram and for body 
fat 9.5 Cals. per gram, although Kohler's average for the 
former is slightly lower, viz., 5.628 Cals. (88). 



The outgo of chemical energy 

Chemical energy supplied in the feed may escape unused 
for either of two reasons: first, the substances carrying it 



230 NUTRITION OF FARM ANIMALS 

may fail to be incorporated into the body, or second, they may 
be incompletely katabolized. 

317. The feces. — Since a greater or less proportion of the 
organic matter of most feeding stuffs fails of digestion and re- 
sorption by farm animals and so does not enter into the body 
proper (148), a considerable amount of unused feed energy 
escapes in the feces, while the excretory products which they 
carry (154) contain chemical energy which has failed of com- 
plete conversion in the body. The chemical energy of the feces 
of farm animals constitutes a very considerable item in their 
total outgo of energy. Its amount can be determined as in 
the case of feeding stuffs by burning a sample, after drying 
with suitable precautions, in a calorimeter and measuring the 
heat evolved. 

318. Combustible gases. — The combustible gases produced 
by fermentation in the digestive tract also carry off relatively 
large amounts of unused chemical energy, the loss in this 
way being precisely analogous to that in the undigested 
matter of the feces except that it escapes in invisible products. 
These gases cannot well be separated from the other gaseous 
excreta for the purpose of making a direct determination of their 
energy. The amounts of carbon and hydrogen excreted in 
them, however, can be determined with the aid of the respiration 
apparatus and on the well-founded assumption that only meth- 
ane and hydrogen are produced the amount of each excreted 
may be calculated. The heats of combustion of both these 
gases being known, the amount of chemical energy which they 
carry off can be readily computed. 

319. Products of incomplete katabolism. — The heat of com- 
bustion of a substance, as already defined, is the amount of heat 
evolved when it is completely oxidized, that is, in the case of 
substances ordinarily occurring in feeding stuffs, when it is 
burned to C0 2 , H 2 0, N 2 , and S0 3 . If the katabolism in the 
body stops short of these end products, the quantity of chemical 
energy transformed is clearly less than the gross energy of the 
substance by an amount equal to the heat of combustion of 
the incompletely oxidized products. 

The proteins of the feed constitute the most important in- 
stance of this sort. All the nitrogen of the digested protein 
and part of its carbon, hydrogen and oxygen, are excreted in 



THE BALANCE OF NUTRITION 231 

the urine in the form of crystalline nitrogenous products, of 
which urea is the most familiar and often the most abundant. 
When these products are burned they yield a certain amount 
of heat, thus showing that they still contain part of the gross 
energy of the protein, and that, therefore, only a portion of the" 
latter has been transformed in the body. 

320. The urine. — In the main, the urine is the vehicle for the 
removal from the body of the incompletely oxidized products 
of katabolism, although some unoxidized or partially oxidized 
material also escapes from the body in the form of the excretory 
products contained in the feces (317), and small amounts of 
chemical energy are contained in the cutaneous excretory 
products (198). 

The energy of the katabolic products contained in the urine 
may be determined as in the case of the feces by burning the 
dried residue in the calorimeter, a small correction being usually 
necessary for unavoidable losses in drying. 

An approximate calculation of the chemical energy of the urine 
may be based upon its nitrogen or better on its carbon content, using 
the average ratio found in experiments on the same species, but these 
ratios vary more or less in different cases, and in exact work direct 
determinations are called for. 

321. Cutaneous excretion. — The amount of chemical energy 
removed in the perspiration is too small to be of any significance, 
except possibly in experiments on severe work. 

In addition to the perspiration there is a continual small loss 
of matter with its accompanying chemical energy in the form 
of epidermal scales, hair, etc., sloughed off. These losses are 
comparable to the excretory products in the feces, since they 
consist essentially of incompletely katabolized body material. 
Their amount is small but is sufficient to be taken account of 
in exact experiments. 

Metabolizable energy 

322. General conception. — It has been shown in the fore- 
going paragraphs that more or less of the chemical energy of 
the feed escapes unused from the body, the total thus rejected 
being equal to the gross energy of the total excreta, solid, liquid 



232 NUTRITION OF FARM ANIMALS 

and gaseous, as measured by their heats of combustion. If, 
then, the gross energy of the total excreta be subtracted from 
the gross energy of the feed, the remainder shows how much 
of the chemical energy of the feed can be metabolized, that is, 
converted into other forms in the organism. To this difference, 
the term metabolizable energy has been applied. 

Metabolizable energy may be briefly defined as the gross 
energy of the feed minus the gross energy of the excreta. Thus 
in the experiment cited previously (294) to illustrate the 
method of determining the balance of matter, the energy content 
of the feed and excreta and the metabolizable energy of the 
total ration were as follows : — 

Energy of feed 

6988 grms. timothy hay 27,727 Cals. 

400 grms. linseed meal 181 1 Cals. 

29,538 Cals. 
Energy of excreta 

16,619 grms. feces *4j243 Cals. 

4357 grms. urine 12 10 Cals. 

142 grms. methane .... 1896 Cals. 

Total 17,349 Cals. 

Metabolizable energy 12,189 Cals. 

It should be observed that the foregoing definition makes no 
assertion whatever as to the forms into which the metabolizable 
energy has been transformed nor as to the degree to which the 
transformation has been of service to the organism. Some of 
the energy, for example, may be retained in the body in a gain 
of fat or protein, as in the illustration just given, i.e., it may 
be temporarily set aside as a reserve to be used later, but it is 
still capable of transformation into other forms and therefore 
constitutes a part of the metabolizable energy. On the other 
hand, the feed might contain some substance capable of oxida- 
tion in the body but of no physiological value to it and which 
was simply burned to get rid of it. The heat thus generated 
might be entirely useless to the animal, yet this energy 
would be part of the metabolizable energy of the feed. Some- 
what similarly, the energy liberated as heat in the methane 
fermentation constitutes part of the metabolizable energy, 
although it does not enter into the tissue metabolism. Metab- 



THE BALANCE OF NUTRITION 233 

olizable energy means simply energy capable of transformation 
in the body. It is the maximum quantity which the feed can 
contribute to the energy changes in the organism. That it 
does not necessarily measure nutritive value is indeed suffi- 
ciently apparent from the method used for its determination. 
As the example already given shows, this does not require any 
measurement of the gain or loss by the animal, but, like a 
digestion experiment, concerns itself simply with the feed and 
the excreta. 

323. Synonyms for metabolizable energy. — Two other 
terms are frequently employed with substantially the same 
significance as metabolizable energy, viz., fuel value and avail- 
able energy. 

Fuel value. — The metabolizable energy of the feed is evi- 
dently capable of conversion into heat in the body. Since a 
considerable portion and sometimes all of it is actually thus 
converted, and since its amount is usually expressed as a matter 
of convenience in heat units, the term fuel value (or physiological 
heat value) has come into use as synonymous with metaboliz- 
able energy. 

The term has the advantage of brevity, but has also certain 
disadvantages. In conjunction with the unit of measurement 
employed, it has a tendency to suggest that the purpose of 
the feed is to supply heat energy and that it is of value 
in proportion as it can do this, which is far from being the 
case. Moreover, there appears to be some danger of confusion 
due to the fact that the same term is used in a different sense 
in relation to fuels. The " fuel value " of a coal, for example, 
means the total amount of heat which it liberates when burned, 
and corresponds, therefore, to the gross energy of a feeding stuff, 
i.e., to its value if used as fuel under a boiler or in a heating 
plant. The fuel value of a feeding stuff, on the other hand, in 
the sense of its metabolizable energy, is the amount of heat 
which it can furnish when oxidized as it is in the body, i.e., more 
or less incompletely. 

Available energy. — A much more unfortunate usage is the 
employment of the term available energy, equivalent to the 
German " Physiologischer Nutzwert" in the sense here assigned 
to metabolizable energy. This usage dates back to Rubner's 
investigations of the replacement values of nutrients in 1882- 



234 



NUTRITION OF FARM ANIMALS 



1885 and to his isodynamic values based upon them. In the 
light of the knowledge available at that time, this use of the 
term was perhaps justified, but as will appear later (369), it has 
since been shown that part of the metabolizable energy of the 
feed is virtually available for heat production alone, while only 
the remainder can be used for general body purposes. If the 
use of the term available energy is to be continued, therefore, 
it becomes necessary to distinguish two degrees of avail- 
ability, using, for instance, the term gross available energy as 
equivalent to metabolizable energy and net available energy 
to signify that part of the metabolizable energy which is avail- 
able for other purposes than heat production. 

In the writer's judgment, simplicity and clearness of concep- 
tion will be promoted by discontinuing altogether the use of the 
term available energy and employing the term metabolizable 
energy, or perhaps fuel value provided the latter is understood 
with the proper restrictions, to designate that portion of the 
gross energy of the feed which is capable of transformation in 
the animal organism. 

324. Factors for metabolizable energy. — Rubner, and 
subsequently Atwater, have proposed factors by the use of 
which the metabolizable energy of the diet of man may be 
computed with a considerable degree of accuracy. 1 

Table 27. — Factors for Metabolizable Energy of Human Food 



Protein . . 
Carbohydrates 
Fats . . . 



Rubner 

Per gram digested 

nutrients 




Atwater 
Per gram total 
nutrients 



Cals. 

4.0 
4.0 
8.9 



The use of these same factors yields approximately correct 
results for carnivora. They have sometimes been applied also 
to the digestible nutrients of the feed of herbivora but without 
sufficient warrant. 



1 Compare the writer's Principles of Animal Nutrition, pp. 272-281. 



THE BALANCE OF NUTRITION 235 



The outgo of work and heat from the body 

325. Outgo of kinetic energy. — The feces, urine, combus- 
tible gases and cutaneous excreta carry off chiefly unused 
chemical energy. 1 To recur to the illustration of the internal 
combustion motor, they are comparable with losses due to 
leakage or incomplete combustion of the fuel. The energy re- 
maining after these losses have been met, i.e., the metabolizable 
energy, may be converted in part into mechanical work and 
in part into heat. 

When an animal performs work, whether in drawing a load, 
carrying a rider, operating a tread power or simply lifting 
the weight of his own body at each successive step, a portion, 
although on the whole a relatively small percentage, of his total 
income of chemical energy is expended in moving objects, i.e., is 
converted into kinetic energy. The kinetic energy thus pro- 
duced may be measured in accordance with the general methods 
described in a previous paragraph (313), usually by conversion 
into gravitation energy and measurement in gravitation units, 
i.e., the gram meter, kilogram meter or foot pound. 

326. Outgo of heat. — The outgo of heat which common 
experience teaches is continually taking place from the bodies 
of men and of animals represents a very considerable share of 
the total income of chemical energy. It has been computed 
that if the heat produced by the average healthy man could 
be prevented from escaping from the body it would in a single 
day raise it to a pasteurizing temperature, while in the course 
of a month at the same rate, the temperature would be raised 
approximately to that of melting cast iron. 

327. Animal calorimeters. — The great variety of animal 
calorimeters which have been devised for the purpose of measur- 
ing the heat production of living animals have been of three 
general types, which may be designated as water calorimeters, 
latent heat calorimeters and emission calorimeters. 

Water calorimeters are those in which the heat is imparted 
to a known quantity of water, the rise of temperature of which 
is measured, i.e., they employ the first of the two methods of 

1 The heat which they also carry off is included in the total outgo of heat con- 
sidered in the next paragraph. 



236 NUTRITION OF FARM ANIMALS 

measuring heat previously described (309). Water calorim- 
eters may be subdivided into those in which the heat is im- 
parted to a stationary mass of water and those called flow 
calorimeters, in which it is taken up by a current of water. 

Latent heat calorimeters make use of the second method of 
heat measurement, viz., causing it to effect a change in the 
physical state of the calorimetric substance. Thus Lavoisier 
employed an ice calorimeter in his experiments upon the re- 
lations between respiration and heat production. This type of 
calorimeter, however, is not well suited to experiments with 
animals and has been but little used. 

Emission calorimeters may be said not to be in a strict sense 
calorimeters at all, i.e., they do not serve directly to measure 
quantities of heat but only to compare the rate of heat pro- 
duction by different sources, but they may be used indirectly 
to measure quantities. The principle of the emission calorim- 
eter may be illustrated as follows : If a known source of heat 
(an electric resistance, for example) be placed in a closed recepta- 
cle located in a room kept at constant temperature, it will tend 
to heat the walls of the container. As the temperature of the 
walls rises, however, heat will be radiated from them with in- 
creasing rapidity until a balance is established between heat 
radiation and heat production and the temperature of the 
walls remains constant. If, now, a second source of heat, 
an animal, for example, be substituted for the first one, 
keeping the external conditions the same, and if it appears that, 
when an equilibrium is reached, the temperature of the walls is 
the same as in the first case, it is concluded that the rate of 
heat radiation is the same as in the first case, and that the 
animal is producing heat at the same rate as was the electric 
resistance, so that the amount of heat produced by the animal 
in a unit of time is thus indirectly measured. 

The respiration calorimeter. — All animal calorimeters used 
for experiments of any length must necessarily be provided 
with ventilation. To prevent a loss of heat in the air current, 
it is introduced at the same temperature as that at which it 
leaves the apparatus. The ventilating air current, however, 
tends to remove water vapor from the chamber and the evapo- 
ration of this water, of course, absorbs a corresponding amount 
of heat as the so-called " latent heat of evaporation " of water. 



THE BALANCE OF NUTRITION 



237 



Either, therefore, evaporation must be prevented by keeping 
the air in the chamber saturated with water, thus introducing 
more or less abnormal conditions, or the amount of water 
carried away in the ventilating air current must be determined. 
If the latter course is followed, it is a relatively simple matter 
to include also determinations of the carbon dioxid and the 
combustible gases excreted, and perhaps of the oxygen con- 




Fig. 34. — Dulong's water calorimeter (Schaefer, Text Book of Physiology). 



sumed. The apparatus then becomes a combination of res- 
piration apparatus and animal calorimeter and hence has been 
called a respiration calorimeter. 

The apparatus used by Dulong in 1822 in his investigation of the 
source of animal heat, the construction of which is shown in Fig. 34, 
may serve to illustrate the form of calorimeter in which a stationary 
mass of water is used. This type of calorimeter has been used in 
various modifications, notably in the United States by Wood, 1 Ott 2 

1 Smithsonian Contributions to Knowledge, No. 23 (1 
2 N. Y. Med. Jour., 49 (1889), 342. 



2 3 8 



NUTRITION OF FARM ANIMALS 




THE BALANCE OF NUTRITION 



239 



and Reichert. 1 It is, however, not readily adapted for use with large 
animals, both on account of the difficulty in determining the true 
average temperature of a large mass of water and on account of the 
great weight of such an instrument. 

The best known and most successful form of flow calorimeter for 
experiments upon animals is that devised by Atwater and Rosa 2 and 




Fig. 36. 

modified by Atwater and Benedict 3 for experiments on man and 
adapted by Armsby and Fries 4 and by Hagemann 5 for experiments on 
the larger farm animals. Figure 35 shows the general appearance of 
the apparatus constructed by Armsby and Fries. 

The most familiar form of emission calorimeter is that of Rubner, 6 
in which the changes in volume of the air enclosed between the double 
walls of the animal chamber constitutes the indicator. Figure 36 
shows the general appearance of the Rubner apparatus. A very 
similar one has been devised by Rosenthal 7 in which the pressure of 
the confined air at constant volume serves as the indicator. 

1 University Med. Mag., 1890, ii, 173. 

2 U. S. Dept. Agr., Office Expt. Stas., Bui. 63 (1899) ; Bui. 136 (1903). 

3 Carnegie Institution of Washington, Publication No. 42 (1905). 

4 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 51, (1903) ; and Experiment Station 
Record, 15 (1 903-1 904), 1037. 

5 Landw. Jahrb., 41 (1911), Erganzbd. I. 

6 Ztschr. Biol., 30 (1894), 91. 7 Arch. (Anat. u.) Physiol., 1894, p. 223. 



240 



NUTRITION OF FARM ANIMALS 



An interesting form of emission calorimeter is the so-called com- 
pensation calorimeter, in which the heat produced by the subject is 
balanced against that produced, for example, by burning pure hydro- 
gen or by an electrical resistance in a precisely similar chamber. 
Calorimeters of this type have been described by Haldane, ' Bohr 2 
and recently by Tangl. 3 

328. Summary. — The foregoing facts may be summarized 
in the following tabular statement showing the several items of 
income and outgo of energy as well as the particular form of 
energy contained in each. 



Income: 


Feed 




Outgo : 








Feces 


Chemical energy 




Urine 






Perspiration 






Combustible gases 






Work 


Kinetic energy 




Heat 


Heat energy 



329. Example of an energy balance. — The same experiment 
upon a steer for which the nitrogen and carbon balance and 
the metabolizable energy (290, 294, 322) have already been 
computed may also serve to illustrate the determination of the 
energy balance. In this experiment the animal performed no 
external work, so that no energy had to be measured in that 
form. 

Table 28. — Daily Energy Balance of a Steer 





Income 


Outgo 


43s7 erms. urine 


Cals. 

27,727 
1811 


Cals. 

14,243 
1210 


Gain by body 


88 
1896 

n,493 
608 








2Q,53 8 


29,538 



1 Jour. Physiol. (London), 16 (1894), 123. 

2 Skand. Arch. Physiol., 14 (1903), 398. 



3 Biochem. Ztschr., 53 (1913), 21. 



THE BALANCE OF NUTRITION 241 

According to the conception of the schematic body (280), 
these figures show that energy to the extent of 608 Cals. was 
stored up in the body as the chemical energy of either protein, 
fat or glycogen. Assuming that there was no change in the 
glycogen content of the animal, the nitrogen and carbon balance 
showed a computed storage of 66.6 grams of protein and 15.2 
grams of fat (294). The average chemical energy of protein is 
5.7 Cals. per gram and that of fat 9.5 Cals. per gram. The 
amounts of energy stored up in the fat and protein gained by the 
steer can therefore be computed as follows : 

In protein 5.7 Cals. X 66.6 = 380 Cals. 

In fat 9.5 Cals. X 15.2 = 144 Cals. 

Total 524 Cals. 

Found from energy balance 608 Cals. 



Difference 84 Cals. 

It thus appears that in this experiment the gain of energy 
found by a direct determination of the energy balance and that 
computed from the balance of nitrogen and carbon agreed 
within 84 Cals., or 0.3 per cent of the total amount of energy 
involved. It is evident that determinations of the nitrogen 
and carbon balance on the one hand and of the energy balance 
on the other may serve as a mutual check, and also that the 
heat production of an animal may be computed quite accurately 
from determinations of the nitrogen and carbon balances (in- 
direct calorimetry.) 



§ 5. Significance of Results 

Studies of the balance of nutrition have played a very promi- 
nent role in both physiological and agricultural investigation. 
Having considered in the foregoing pages the general methods 
of the balance experiment, a brief consideration of the signifi- 
cance of the results obtained by their use as compared with those 
reached by other methods seems called for. 

330. Comparison with metabolism investigations. — The 
results of experiments like the one with a steer used as an 
illustration in previous paragraphs show, within the limits of 
experimental error, the loss or the storage of chemical energy 



242 NUTRITION OF FARM ANIMALS 

resulting from the use of a certain feed or ration and approxi- 
mately in what kind of material (protein, fat, glycogen) the 
energy lost or gained was contained. The balance experiment, 
therefore, is adapted to determine the total nutritive effect of 
a given substance, while if the comparative slaughter test be 
regarded as a form of balance experiment (284) the particular 
organs or tissues in which gain or loss took place can be deter- 
mined. 

The balance experiment, however, affords no insight into the 
details of the chemical mechanism by which the observed nu- 
tritive result is brought about. For example, balance experi- 
ments have demonstrated that starch may serve as a source of 
fat and have shown quantitatively the amount of fat formed 
from a given weight of starch. As applied to known chemical 
compounds, such a result as this is perfectly definite and of the 
highest value, but it gives absolutely no information as to the 
intermediate steps of fat formation, either in the processes of 
digestion, resorption or metabolism. 

On the other hand, investigations of the intermediary metab- 
olism, like those whose main results have been outlined in 
Chapter V, have necessarily been to a large extent qualitative. 
They have demonstrated some of the steps through which the 
various anabolisms and katabolisms occur, but as a rule have 
not attempted to deal directly with quantitative questions. 1 

Naturally the foregoing comparison is neither comprehensive nor 
exclusive. It aims simply to point out a broad general distinction 
between two types of nutrition investigation which in reality shade 
into each other. 

Balance experiments have sometimes been characterized, 
with a certain half contemptuous implication, as " bookkeeping 
with the body." The characterization is a good one but the 
implication is unwarranted. It is perfectly true, as some critics 
of the balance experiment point out, that, for example, the most 
accurate record of the income of raw materials and outgo of 
finished products would of itself give a very incomplete notion 
of the operations of a great factory and that the successful 
conduct of such an enterprise requires as intimate a knowl- 

1 For a summary of some of the more important of these methods compare 
Dakin, Oxidations and Reductions in the Animal Body, Chapter III. 



: 



THE BALANCE OF NUTRITION 243 

edge as possible of the functions of each separate machine 
and of the changes undergone by the materials submitted to 
its action. 

It may fairly be presumed, however, that these critics, even 
with the fullest knowledge of the technical details of such a 
factory, would hardly undertake to conduct it as a business 
enterprise without keeping account of the stock purchased and 
the output realized, i.e., exactly the sort of bookkeeping which 
the balance experiment attempts for the animal body. The 
truth is that both types of investigation are equally necessary 
and each aids in the interpretation of the other. The balance 
experiment has been especially prominent in the past, while at 
present attention is being directed to a greater extent to in- 
vestigations of the intermediary metabolism, but neither can 
say to the other " I have no need of thee." 

331. The balance experiment in agricultural investigations. 
— As already indicated, the methods of the balance experiment 
have been quite largely applied in agricultural investigations. 
Such investigations have been made, in the majority of cases, 
not with single chemical compounds, but with feeding stuffs 
or rations as a whole, and the effect observed in such an ex- 
periment is obviously a summation of the effects of all the 
ingredients contained in the feed consumed. The result, there- 
fore, while entirely adequate to determine the total nutritive 
effect of the particular material experimented with is less capable 
of generalization than one obtained with a single chemical 
compound like starch or fat, and from this point of view may 
even be regarded as being in a sense empirical. A compre- 
hensive knowledge of the nutritive value of a feeding stuff im- 
plies, first, a determination of the kinds and amounts of chemical 
compounds contained in it and, second, a determination of the 
exact physiological functions of each. Obviously, however, 
such a complete determination of the nutritive value of any 
considerable number of feeding stuffs is a work requiring a vast 
expenditure of time and labor. One justification, therefore, for 
the " short-cut " method of determining summarily by a bal- 
ance experiment the effect of a feeding stuff or ration is that it 
appears possible to secure in this way within a reasonable time 
data which can be put to practical use in the comparison of 
feeding stuffs and rations. Moreover, it is to be anticipated 



244 NUTRITION OF FARM ANIMALS 

that the conclusions as to the nutritive value of any material 
drawn from even the most elaborate chemical and physio- 
logical investigations will need finally to be checked and con- 
firmed by the methods of the balance experiment. 

The value of the balance experiment in relation to stock 
feeding, however, is far from being limited to the summary 
determination of the total nutritive values of feeding stuffs, 
although it has rendered important service in that field. 

As will become apparent in Part III, the feed requirements 
for animals for various purposes, as well as the general physio- 
logical laws governing the processes of maintenance, growth, 
fattening, milk production, the performance of work, etc., can 
be successfully studied only with the aid of balance experi- 
ments, and the results obtained in such experiments are of 
general scientific value independent of the particular feeding 
stuff used. A striking illustration of the importance of such 
investigations on farm animals is afforded by the results ob- 
tained by Zuntz and his associates, by Kellner and others re- 
garding the expenditure of energy in the digestion and assimi- 
lation of the feed (365-370). The marked differences between 
these animals and man or carnivora as regards the character 
of the feed and of the digestive processes have served to make 
prominent certain factors of the so-called " work of digestion " 
which were inconspicuous in the lattei subjects and thus the 
investigations have yielded important contributions to com- 
parative physiology. 

332. Comparison with practical experiments. — Finally, it 
should be observed that the methods of exact feeding experi- 
ments based on a determination of the balance of matter and 
energy do not differ in their ultimate logical basis from those of 
so-called " practical " experiments. In both cases, the meas- 
ure of the nutritive value of a feeding stuff, of the influence of 
changed conditions, or of the efficiency of the animal as a food 
producer, is the effect upon the animal. The difference lies 
in the accuracy and degree of detail with which that effect is 
determined. The reasons for the inadequacy of the live weight 
as a measure of nutritive effect have already been considered 
(281-283), while the experience of more than 50 years has 
sufficiently demonstrated that the attempt to measure nutritive 
effects by changes in the weight of the animal or by the gross 



THE BALANCE OF NUTRITION 245 

product yielded fails to give results which are consistent with 
each other or which permit of the formulation of general prin- 
ciples. Only the laborious methods of the balance experiment 
or the refinements of physiological investigation can be relied 
upon to reveal those fundamental laws upon which the suc- 
cessful practice of stock feeding depends. 



PART III 
THE FEED REQUIREMENTS 



CHAPTER VII 
THE FASTING KATABOLISM 

333. Significance. — It is a familiar fact that in the absence 
of feed the life of the animal can be supported for a time at the 
expense of the materials of the body itself. If sufficient water 
and oxygen be supplied, those metabolic processes by which 
energy is liberated for the physiological activities of the body 
(201, 207) may continue for a considerable period, although, of 
course, they are ultimately halted by lack of material or im- 
pairment of the integrity of the protoplasm. The fasting 
animal in a state of rest, therefore, affords an opportunity to 
study the demands of the fundamental vital processes un- 
complicated by the functions of digestion and resorption or by 
the requirements of growth, fattening or reproduction. 

A qualitative and quantitative knowledge of the expenditure 
of matter and of energy by the fasting animal, then, is obviously 
an important step towards ascertaining the supply of feed 
necessary for various purposes. 

334. Substances katabolized. — All the principal compo- 
nents of the body may be katabolized and yield energy for the 
support of the fasting organism. 

Fat. — It is a familiar conception that fat formation is the 
body's method of disposing of surplus feed, and that the body 
fat is a store of reserve fuel material. The converse of this 
fact is equally familiar. The fasting or insufficiently fed ani- 
mal loses fat, and may reach a stage of extreme emaciation be- 
fore the active tissues fail to perform their functions. Obviously, 
the fasting animal lives largely upon its reserve of fat. These 
conclusions from common observation have been fully con- 
firmed by comparative analysis of the carcasses of well-fed and 
of fasted animals as well as by the results of balance experiments 
in which the exact nature of the outgo from the body has been 
determined. 

Carbohydrates. — In addition to fat the body contains more 
or less non-nitrogenous matter in the form of glycogen in the 

249 



25° 



NUTRITION OF FARM ANIMALS 



liver and muscles. During the first few days of fasting, this 
store of carbohydrates is also drawn upon, as is indicated by 
the fact that the respiratory quotient tends to approach unity, 
while later the amount of glycogen katabolized becomes very 
small. 

Protein. — Balance experiments, however, while confirming 
the conclusion that the loss of tissue in fasting usually consists 
chiefly of fat together with some carbohydrates, show that there 
is also a continual katabolism of body protein and a corre- 
sponding excretion of urinary nitrogen. While the energy 
expended by the fasting animal is derived chiefly from the 
breaking down of non-nitrogenous material, the functional 
activities of the body necessarily involve the katabolism of a 
certain minimum amount of protein. 

Ash. — Finally, in addition to those groups of substances 
whose katabolism yields energy to the body, the so-called min- 
eral elements, or ash, of the body take part in the processes of 
katabolism and are continuously excreted in the urine of the 
fasting animal. 

The foregoing facts are well illustrated by Benedict's l inves- 
tigations upon inanition. The average results of a number of 
experiments in which men fasted for from two to seven con- 
secutive days were as follows : — 

Table 29. — Average Katabolism of Fasting Men 







O "2 
W W 

a w 


Total Katabolism 


Katabolism per Kilo- 
gram Body Weight 




Protein 


Fat 


Glycogen 


Protein 


Fat 


Glyco- 




& m 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


First day .... 


14 


60.2 


i35-i 


IIO.O 


O.94 


2.IO 


I.69 


Second day 




14 


76.6 


165.9 


40.3* 


1. 21 


2.6l 


0.62* 


Third day . 




6 


78.5 


155-2 


21.8 


1.28 


2-54 


0.36 


Fourth day 




5 


68.6 


147.2 


23-3 


i-i5 


2.47 


O.40 


Fifth day . 




2 


62.6 


146.4 


8.2* 


1. 11 


2.6l 


O.14* 


Sixth day . 




1 


64.4 


129.8 


21.7 


1. 14 


2.30 


O.38 


Seventh day 




1 


60.8 


132.5 


18.7 


1.08 


2.36 


0.33 



1 The Influence of Inanition on Metabolism ; Carnegie Institution of Washington, 
Publication No. 77 (1907), pp. 456-464. 

* Omitting one case in which a small gain of glycogen was observed. 



THE FASTING KATABOLISM 



251 



§ i. The Protein Katabolism in Fasting 

335. Protein katabolism normally small. — In view of the 
structural functions of the proteins (264), it is of some im- 
portance to inquire what proportion of the total energy require- 
ment is supplied by these substances. 

This aspect of the subject has been considered especially by 
E. Voit, 1 who has compiled and discussed the results of a con- 
siderable number of experiments upon fasting. While some of 
his computations are based on estimates, they are sufficiently 
accurate to outline definitely the main features of the fasting 
katabolism. They show that in what may be spoken of as the 
normal fasting animal, in which the influence of the previous 
feeding has disappeared and in which, on the other hand, the 
fat reserve has not been exhausted, the protein katabolism sup- 
plies a rather small proportion of the total energy transformed, 
the percentage with dogs, e.g., ranging in the majority of cases 
between 10 and 17. 

336. Fasting protein katabolism variable. — It is not true, 
however, as has sometimes been loosely stated on the basis of 
C. Voit's experiments (338), that the protein katabolism of a 
fasting animal becomes constant within a short time. On the 
contrary, in the presence of an adequate amount of body fat, 
its amount tends to diminish with the progress of fasting. For 
example, in one of Benedict's fasting experiments (Table 29), 
the total urinary nitrogen upon the several days of the experi- 
ment was : — 



Table 30. — Protein Katabolism of a Fasting Man — Benedict 



Days 


Urinary Nitrogen 


Days 


Urinary Nitrogen 


Total 


Per kilogram 
weight 


Total 


Per kilogram 
weight 


1 
2 
3 
4 


Grams 

12.24 
12.45 
13.02 
11.63 


Grams 

0.206 
.211 
.223 
.202 


5 
6 

7 


Grams 

10.87 
10.74 
10.13 


Grams 

O.191 
.190 
.181 



1 Ztschr. Biol., 41 (1901), 167. 



252 



NUTRITION OF FARM ANIMALS 



337. Influence of body fat. — E. Voit's compilation (335) 
likewise showed clearly that the ratio of protein to total katab- 
olism in fasting may vary considerably as between individuals, 
depending on the relative amount of fat contained in the body. 
So long as body fat is readily available as fuel, the amount of 
protein katabolized remains relatively small, but if the animal is 
originally deficient in fat, or if its content of fat becomes much 
reduced during fasting, more protein is katabolized to make up 
for the deficiency. 

Usually, the store of fat in the body is less than that of protein, 
while in fasting its exhaustion is relatively more rapid. There comes 
a time, therefore, when the supply of non-nitrogenous material to the 
tissues begins to flag. When this happens, the protein katabolism 
begins to increase ; that is, when the supply of reserve fuel material 
runs low, the organism begins to use more of the protein of its tissues 
as a source of energy, and Voit 1 has shown that this occurs whenever 
the ratio of fat to protein remaining in the body falls below a certain 
limit. If the animal was originally well nourished, this rise in the 
protein katabolism occurs only shortly before death, from which it 
has received the name premortal rise. In the case of very fat ani- 
mals this point may never be reached, while, on the other hand, in a 
lean animal the protein katabolism may increase steadily from the 
very beginning of the fasting. The following three experiments 
upon a fat guinea pig, a medium fat dog and a lean rabbit, cited by 
Voit from Rubner's experiments, serve to illustrate these three types 
of fasting katabolism. 

Table 31. — Fasting Protein Katabolism of Fat, Medium and Thin 

Animals 



Guinea Pig 


Dog 


Rabbit 


Day of 
Fasting 


Protein Katab- 
olism in Per Cent 
of Total Katab- 
olism 


Day of 

Fasting 


Protein Ka- 
tabolism in Per 
Cent of Total 
Katabolism 


Day of 
Fasting 


Protein Ka- 
tabolism in Per 
Cent of Total 
Katabolism 


2 


IO.4 


2-4 


16.3 


3 


16.5 


3 


II. I 


10-11 


I3-I 


5-7 


23.6 


4 


II.O 


12 


15-5 


9-12 


26.5 


5 


II.Q 


13 


17.4 


13-15 


29.8 


6 


11.8 


14 


20.0 


16 


50.I 


7 


6.9 






17-18 


96.4 


8 


II. 2 










9 


IO.9 











1 Ztschr. Biol., 41 (iqoi), 502. 



THE FASTING KATABOLISM 



253 



338. Influence of previous protein feeding. — The classic 
experiments of Carl Voit * upon fasting dogs have shown that 
the protein katabolism in the early days of fasting may vary 
widely according to the amount of protein previously consumed. 
When the fasting follows a high protein ration, the protein 
katabolism on the first day of fasting may be relatively large, 
but it soon falls to a comparatively low level which is approxi- 
mately the same whatever the initial ration. This behavior is 
well illustrated by the following results, all upon the same 
animal, which have been fully confirmed by numerous sub- 
sequent experiments 

Table 32. — Protein Katabolism of Fasting Dog — Voit 







Previous Feeding 






1800 










2500 


Grams 


1500 


1500 






Grams 


Meat, 


Grams 


Grams 


Bread 




Meat 


250 Grams 
Fat 


Meat 


Meat 






Grams 


Grams 


Grams 


Grams 


Grams 


Urinary nitrogen 2 per day 












Last day of feeding . . 


84.4 


60.7 


5i-7 


51-7 


H-5 


First day of fasting . 




28.1 


17-5 


13-9 


12.4 


9.1 


Second day of fasting 




11.6 


10. 9 


8-5 


8.7 


7-3 


Third day of fasting 




8. 9 


7.8 


8.2 


7-3 


7.0 


Fourth day of fasting 




8.1 


6.9 


7.0 


7.0 


6.2 


Fifth day of fasting 




5-7 


5-9 


6.6 


6.9 


5.9 


Sixth day of fasting . 




6.2 


6.0 


6.1 


6.0 


6.1 


Seventh day of fasting 




5-8 


5-6 


5-6 


6.0 




Eighth day of fasting 




4-7 




6.0 


5-6 




Ninth day of fasting 










5-6 




Tenth day of fasting 










5-3 





Furthermore, the high protein katabolism which is observed 
during the first two or three days of fasting after high protein 
feeding is accompanied by a relatively smaller katabolism 
of fat. Thus, in the first of the foregoing experiments respira- 
tion trials were made on the second, fifth and eighth days with 
the following results : — 



1 Ztschr. Biol., 2 (1866), 307. 



2 Computed from Voit's figures for urea. 



254 



NUTRITION OF FARM ANIMALS 

Table 33. — Total Katabolism oe Fasting Dog 



Second day 
Fifth day . 
Eighth day 



Urinary 
Nitrogen 



Grams 

1 1.6 

5-7 
4-7 



Fat Katabo- 
lized 



Grams 

86 
103 
99 



Protein Katab- 
olism in Per 

Cent of Total 
Katabolism 



% 

26.2 
12.7 
11. 1 



Obviously, we have here the reverse of what takes place in 
the later days of fasting, viz., a gradual substitution of fat for 
protein as the readily available supply of the latter in the body 
is reduced. Doubtless the effect would have been found to 
be still more marked on the first day of fasting, when the pro- 
tein katabolism was equivalent to 28.1 grams of nitrogen. 

339. Physiological minimum of protein. — The facts re- 
corded in the previous paragraphs render it evident that the 
lowest level of protein katabolism is not necessarily attained 
during complete fasting. Although the protein katabolism of 
a fasting animal soon reaches a comparatively low level which 
changes but slowly, nevertheless its amount may be greatly 
affected, on the one hand by the amount of protein previously 
consumed, and on the other hand by the stock of non-nitrogenous 
material (fat and glycogen) contained in the body. While 
normally some 10 to 17 per cent of the energy metabolized 
in complete fasting is derived from protein (335), the proportion 
may rise to twice this amount on a day following heavy protein 
feeding, or to almost 100 per cent in case of an animal whose 
stock of body fat is exhausted. In such cases it is evident that 
part of the protein is katabolized simply for the sake of supply- 
ing energy, since the smaller amounts katabolized in what may 
be called a normal or average condition of the fasting animal 
are at least sufficient to maintain all the vital functions, the 
latter proceeding for a considerable time in a substantially 
normal manner. 

The level of protein katabolism being so dependent on the 
amount of non-nitrogenous material available as a source of 
energy, the question naturally arises whether by supplying an 



THE FASTING KATABOLISM 255 

animal with liberal amounts of non-nitrogenous nutrients, but 
no protein, the protein katabolism might not be reduced to an 
amount even smaller than that observed in the absence of all 
feed. Experiments by C. Voit and by Rubner on dogs and by 
Landergren, Folin and Cathcart on man have shown this to 
be the case with these species. 

Comparisons of this sort on farm animals are not readily 
made, especially with herbivora, and none have yet been re- 
ported, but McCollum and Steenbock l have shown that the 
protein katabolism of the pig may be reduced by long continued 
feeding on a non-nitrogenous diet (starch) to an amount materi- 
ally less than appears to be necessary in the feed of the animal 
under ordinary conditions to maintain nitrogen equilibrium 
(417), the average of all of their experiments being equivalent 
to 0.28 lb. of protein per 1000 lbs. live weight. 

340. Functions of protein in fasting. — The fact that a 
certain minimum katabolism of body protein persists even in 
the presence of the most abundant supply of non-nitrogenous 
nutrients has generally been interpreted in the past as showing 
that a certain amount of the protein of the cell is necessariiv 
broken down in the performance of its physiological functions. 
This necessary minimum has been somewhat vaguely compared 
to the wear of a machine, Rubner especially designating it as 
the " wear and tear " quota of the protein katabolism. More 
recent investigations, however, have suggested the possibility 
of another explanation. 

The actual nitrogenous nutriment of the body cells is not 
proteins as such, but substantially the simple amino acids out 
of which they are built up. As required, these amino acids 
may be synthesized to protein (226, 232), but there appears to 
be some reason for believing that they may also be necessary 
for other purposes in the body ; that certain of them may, for 
example, as was suggested by Willcock and Hopkins, be essential 
to the production of the various internal secretions and hormones 
which apparently play so large a part in metabolism. If, how- 
ever, the normal performance of the body functions calls for 
a supply of some particular amino acid, tryptophan e.g., this 
can be derived, in the fasting animal, only from the cleavage of 
body protein, since there is no evidence that tryptophan can 
1 Wis. Expt. Sta., Research Bui. No. 21, p. 55. 



256 NUTRITION OF FARM ANIMALS 

be synthesized by the organism. It might very well be, there- 
fore, that the minimum unavoidable protein katabolism in the 
absence of nitrogenous feed is due to such a demand for certain 
amino acids or other groupings, and only in part or not at all 
to a necessary breaking down of cell proteins as a condition of 
protoplasmic activity. Moreover, it is quite conceivable that 
both of these views may be true ; that a part of the minimum 
protein katabolism represents a necessary destruction of cell 
protoplasm in the performance of its functions, while the other 
part represents protein broken down for the sake of securing 
certain constituents for specific purposes. 

There will be occasion to consider these possibilities further 
in discussing the protein requirement for maintenance (398). 

§ 2. The Energy Katabolism in Fasting 

341. Internal work. — The body of an animal receiving no 
feed and doing no external work is still carrying on a great 
variety of internal activities, both mechanical and chemical. 
Of the former, the most prominent is the muscular work of 
circulation and respiration, together with the maintenance 
of muscular tonus (632), while the secretory and excretory 
activities of the various glands are typical of the latter. These 
various bodily activities, whose due performance is essential 
to the continued existence of the animal, may be conveniently 
summarized in the term internal work. 

342. Measure of energy expended in internal work. — In 
the fasting animal, all the various forms of internal work in- 
dicated in the previous paragraph are performed by means of 
energy derived from the katabolism of the fats, carbohydrates 
and proteins contained in the tissues. The chemical energy 
thus utilized may undergo numerous transformations, but 
ultimately, since it does no work upon the surroundings of the 
animal, it assumes the form of heat. A determination of the 
heat produced by a fasting animal in a state of rest, therefore, 
furnishes a measure of the energy expended in internal work, 
or of what is often called the basal metabolism. 

343. Relative constancy of energy katabolism. — The results 
recorded in § 1 regarding the nature of the material katabolized 
in fasting, and the way in which fat, carbohydrates and protein 



THE FASTING KATABOLISM 



257 



may mutually replace each other as fuel material according as 
one or the other is most available, render it evident that the 
controlling factor in the katabolism of the fasting body is the 
demand for energy for the performance of the internal work and 
can hardly have failed to suggest that this demand must be 
relatively constant in the same individual under like conditions. 
That such is in fact the case has been demonstrated by a large 
number of experiments. While not mathematically invariable, 
the fasting katabolism, expressed in terms of energy, tends 
to approach a uniform value in proportipn as the experimental 
conditions are maintained constant. The fasting organism 
requires approximately the same quantity of energy from day 
to day for the performance of its necessary internal work, but 
seems more or less indifferent as to whether this energy is 
derived from the katabolism of fats, carbohydrates or proteins. 

For example, in Voit's experiment cited in the previous section to 
illustrate the interrelations of protein and fat katabolism (Table 33), 
the computed energy of the protein and fat katabolized on each of 
the three days was as shown in the following table, from which it 
appears that the total energy katabolism, especially when computed 
per kilogram of live weight, was approximately the same on the 
different days. 

Table 34. — Energy Katabolism of Fasting Dog 



Second day 
Fifth day 
Eighth day 



Live 
Weight 



Kgs. 

32.87 
31.67 
3Q-54 



Energy 

from 
Protein 



Cals. 

289.3 
142.2 
117. 2 



Energy 
from 
Fat 



Total 
Energy 



Cals. 

816.9 

978.5 
942.4 



Cals. 
1106.2 
1120.7 
1059.6 



Total 
Energy 

per Kg. 
Live 

Weight 



Cals. 

33- 66 
35-38 
34-70 



The same thing is true of Rubner's determinations of the fasting 
katabolism of a rabbit, a dog and a guinea pig, whose results as re- 
gards the protein katabolism have been already considered (337) and 
likewise of Benedict's investigations upon fasting men (334). 

344. Energy expenditure in fasting a measure of main- 
tenance requirement. — In the fasting animal in a state of 
s 



258 NUTRITION OF FARM ANIMALS 

complete rest and at moderate external temperature, the vital 
activities are evidently reduced to the minimum compatible 
with the continuance of life. Since the internal work of such 
an animal is performed at the expense of the chemical energy- 
stored up in its tissues, the body's stock of energy is being 
constantly depleted by an amount equivalent to the internal 
work done and this loss of energy must be made good from the 
feed if the animal is to be maintained. The relatively constant 
total katabolism of the fasting animal, as expressed in its heat 
production, is therefore the measure of the amount of energy 
expended in carrying on the fundamental vital activities of 
the body, and consequently of the minimum quantity which must 
be supplied in a maintenance ration. 

§ 3. Conditions Affecting the Fasting Katabolism 

345. Size of animal. — That large animals katabolize more 
matter and produce more heat than smaller ones, and therefore 
require more feed for maintenance, needs no special proof. Ex- 
periment shows, however, that the difference is not propor- 
tional to size or weight, but that small animals have a more 
intense katabolism than large ones, its amount being approxi- 
mately proportional to the body surface, which, of course, is 
relatively greater in the smaller animal. 

The relation to body surface appears to have been first suggested 
by Bergmann (cited by Rubner) in 1852 and later by Miintz * in 1878, 
but Rubner 2 seems to have made the first, quantitative investigation 
of the question, determining the fasting katabolism of six dogs whose 
weights ranged from 3 to 24 kilograms. 

While not mathematically constant, the ratio between the fasting 
katabolism and surface showed a close approximation to uniformity, 
and the same fact has been verified by a considerable number of in- 
vestigators, although with some exceptions, and is now generally ac- 
cepted. Moreover, it has been shown 3 to be approximately true not 
only of animals of the same species but of animals ranging in size 
from man to domestic fowls and including also cold blooded animals. 

346. Computation of katabolism per unit of surface. — It 
is a familiar fact that the surfaces of solids of the same shape, 

1 Ann. Inst. Agron., Ill, p. 59. 2 Ztschr. Biol., 19 (1883), 535. 

3 E. Voit; Ztschr. Biol., 41 (1901), 113. 



THE FASTING KATABOLISM 259 

i.e., of those which are geometrically similar figures, are propor- 
tional to the two-thirds powers of their volumes. Since the 
specific gravity of animals varies but slightly, it may be said 
without material error that the body surfaces of animals of the 
same shape are proportional to the two-thirds powers of their 
weights. This relation may be expressed by the following for- 
mula, proposed by Meeh, 1 in which W equals the weight in 
grams, S the surface in square centimeters, and k is a factor 
which is constant for all animals of the same shape. 

5 = kWl 

The value of the constant k for the horse as reported by 
Hecker is 9.02. Trowbridge, Moulton and Haigh 2 have de- 
termined the value of k for 35 Hereford-Shorthorn cattle of 
various ages from birth up and in various conditions of fatness, 
using the empty weight as a basis. Dividing the animals into 
groups they found the following average values : — 

Table 35. — Values of k for Beef Cattle 

Young and thin animals . . . ' 9.92 

Animals in medium condition 9.41 

Fat animals 18 months old or less 8.57 

Fat animals two years old or more 7.65 

According to these investigators the empty weight of cattle 
constitutes the following percentages of their live weight : — 

Table 36. — Empty Weight as Percentage of Live Weight 

Show cattle 9 2 ~94 per cent 

Fat cattle 91 

Medium cattle 89-90 

Thin cattle 87-89 

With the aid of the foregoing factors the total katabolism 
of beef cattle, and perhaps of other types, as determined by 
experiment may be computed per unit of body surface with 
reasonable accuracy. It is apparent that comparisons based 
upon the live weight instead of the empty weight would also 
be substantially accurate for thin and medium cattle. No 
similar data exist for other species of farm animals. 

1 Ztschr. Biol., 15 (1879), 425. 2 Mo. Expt. Sta., Research Bui. 18. 



260 NUTRITION OF FARM ANIMALS 

The principal cause of the difference between the groups of cattle 
appears to be the variation in the proportion of fat to active tissue, 
and Moulton * has shown that if this be eliminated by making the 
fat-free empty weight the basis of computation, an average value of 
10.34 for k gives results very closely approximating those actually 
observed. He likewise finds that the body surface of thin and medium 
cattle is somewhat more closely proportional to the five-eighths than 
to the two-thirds power of the empty weight, while for fat cattle the 
five-ninths power gives the closest agreement, the corresponding 
values of k being respectively 11.86 and 13.40. 

347. Computation of katabolism to standard weight. — It 

is often desirable to compare the katabolism of animals of dif- 
ferent weights or to compute experimental results to some 
convenient standard weight. Such comparisons should evi- 
dently be made on the basis of body surface rather than of body 
weight. Few actual determinations of the body surface of 
animals have been made, how T ever, and with the exception of 
the horse and of beef cattle none on farm animals, so that it is 
in many cases impracticable to express the katabolism of the 
latter per unit of surface. For purposes of comparison between 
individuals of the same species and type, however, at least 
approximate results may be secured on the assumption that 
the animals to be compared are geometrically similar, so that 
their bpdy surfaces are substantially proportional to the two- 
thirds powers of their weights. For example, a steer weighing 
1283 pounds was found to have a computed fasting katabolism 
(374) of 8671 Cals. It is often a matter of convenience to com- 
pute such a result to a weight of 1000 pounds. A steer weigh- 
ing 1000 pounds, other things being equal, would have a smaller 
katabolism in proportion to its smaller surface. The ratio 
between the surfaces of the two animals would be approximately 
1000*: 1283% and the fasting katabolism of the smaller animal 
would therefore be 8671 Cals. X (f!nrf) ! = 7345 Cals. In 
this way it is easy to compute the relative katabolism of dif- 
ferent individuals without the necessity of expressing it per 
unit of surface. 

Of course, such a comparison is only an approximation. In 
particular, as has just been shown (346), different animals are 
not of the same shape. The young animal differs in conforma- 

1 Jour. Biol. Chem., 24 (1916), 299. 



THE FASTING KATABOLISM 261 

tion from the older one and the fat from the thin one and the 
beef steer and dairy cow, e.g., are far from being geometrically 
similar. Additional determinations of the relation of surface 
to weight in different species, types and ages of domestic ani- 
mals would be of much interest but in their absence the method 
of comparison just outlined may probably be assumed to give 
a fair approximation to the truth and is certainly more accurate 
than a simple computation in proportion to weight. 

348. Muscular activity. — As was implied in the introductory 
section of Chapter VI (274), and as will appear in greater detail 
in Chapter XIV, muscular work is done at the expense of energy 
derived from the katabolism of body substance, and no other 
single factor so largely influences the total katabolism. The 
minimum fasting katabolism which represents the demands of 
the indispensable life processes is exhibited only in a state of 
complete muscular rest. It is rarely the case, however, that an 
animal, even when at rest in the ordinary sense, does not main- 
tain more or less muscular tension or execute more or less mo- 
tions of various parts of the body, all of which, even when 
apparently slight, involve in the aggregate considerable ex- 
penditure of energy. 

Zuntz and Hagemann, 1 for example, report a respiration experiment 
upon a horse in which the uneasiness caused by the presence of a few 
flies in the chamber of the apparatus caused an increase of 10 per 
cent in the metabolism. Johansson 2 found the hourly excretion of 
carbon dioxid by a fasting man when simply lying in bed (awake) 
to be 24.94 grams as compared with 20.72 grams when all the muscles 
were as perfectly relaxed as possible. Benedict and Carpenter 3 have 
compared the metabolism of men during sleep with that of the same 
subjects lying quietly in bed immediately after waking. In the three 
cases which they regard as strictly comparable the increase in the 
heat production during the waking period ranged from 5.8 to 15.2 
per cent, averaging 11. 4 per cent. Benedict and Talbot, 4 in experiments 
upon infants, found that even scarcely noticeable muscular activity 
produced a most marked effect on the carbon dioxid excretion, and 
Benedict and Pratt 5 have noted similar results with dogs. 

1 Landw. Jahrb., 23 (1894), 161. 

2 Skand. Arch. Physiol., 8 (1898), 85. 

3 Carnegie Institution of Washington, Publication No. 126 (1910), p. 241. 

4 Amer. Jour. Diseases of Children, 4 (1912), 129. 
6 Jour. Biol. Chem., 15 (1913), 1. 



262 NUTRITION OF FARM ANIMALS 

Since comparatively insignificant movements have such a 
striking effect upon the total katabolism, it is evident that the 
amount of muscular activity must be an important factor in 
determining the relative energy requirements of two animals 
even though their minimum katabolism in a state of absolute 
rest may be identical. In experiments of any considerable 
duration on normal animals, it is impossible to avoid more or 
less expenditure of energy in this incidental muscular work, 
while it is often a matter of difficulty to make the different 
periods of an experiment comparable in this respect. 

349. Standing and lying. — Considerable muscular exertion 
is required during the waking hours to maintain the relative 
position of the different members of the body. This is es- 
pecially true of standing. It has been shown that a man or an 
animal when standing excretes notably more carbon dioxid 
than when resting or lying down and produces correspondingly 
more heat. Differences of as much as 25 per cent have been 
observed in man and of 30 to 40 or more per cent, in cattle. It 
is evident, then, that if one animal lies down for twelve hours 
and another for only eight hours during the twenty-four, the 
former will, other things being equal, require less feed energy 
for actual maintenance than the latter. 

350. External temperature. — Farm animals belong to that 
general class known as warm blooded, or homoiothermic, animals, 
whose bodies during health maintain a nearly constant tempera- 
ture which is higher than that of their usual surroundings. The 
so-called " animal heat " is being continually generated by the 
katabolism going on in the body, while on the other hand the 
animal is continually imparting heat to its surroundings in four 
principal ways : viz., by conduction, by radiation, by evapora- 
tion of water, and as the sensible heat of the excreta. 

Since the animal is both producing and losing heat continu- 
ally, the maintenance of a constant body temperature implies 
the existence of some regulative mechanism by means of which 
the production and emission of heat may be adjusted to each 
other. This adjustment is effected in general in two ways which 
may be called, respectively, physical and chemical regulation. 

351. Physical regulation of body temperature. — Changes 
in the temperature of its surroundings, in the relative humidity 
of the air, etc., tend to produce the same effect upon the animal 



THE FASTING KATABOLISM 263 

as upon an inanimate body. A fall of temperature, for example, 
tends to increase the rate of outflow of heat and a rise of tem- 
perature to diminish it. In the so-called physical regulation, 
these tendencies are offset and the rate of heat emission main- 
tained constant chiefly by means of changes in the temperature 
and state of moisture of the skin, brought about on the one 
hand by an adjustment of the blood flow and on the other 
through the perspiration. 

The tendency of a rise of external temperature to check 
the outflow of heat is compensated for by a vaso-motor reflex 
which causes the arterioles leading to the surface of the body to 
relax (187), so that more blood flows through the skin capillaries, 
thus tending to raise the temperature of the surface and increase 
the outflow of heat. This phenomenon is readily observed 
in the flush which follows exposure to high temperatures. This 
method of regulation might be compared to opening the win- 
dows of a heated room to cool it. 

If the external temperature continues to rise, visible per- 
spiration occurs, or in the case of animals which have no sweat 
glands, like the dog, a peculiar form of breathing sets in and 
relatively large amounts of water are evaporated from the skin 
or from the tongue and the interior of the mouth and throat. 
In this way, large quantities of heat are carried off as the latent 
heat of vaporization of water, somewhat as an overheated room 
may be cooled by sprinkling the floor. 

If the externa] temperature falls again, the process is reversed. 
Sensible perspiration decreases, the blood is diverted from the 
capillaries of the skin to the internal capillaries, and if the change 
takes place too rapidly, may even lead to congestion of the latter. 
The process is analogous to closing the -windows of a room as 
the weather grows colder. 

352. Chemical regulation of body temperature. — There 
are evidently limits to the possibilities of physical regulation. 
On the one hand, the external temperature may rise so high 
that it is impossible for the heat to escape from the body as fast 
as it is produced by the necessary katabolism, and heat apoplexy 
results. On the other hand, the temperature may fall so low 
that the utmost restriction of evaporation and the greatest 
possible diversion of the blood from the superficial capillaries 
is insufficient to conserve the body temperature. If the windows 



264 NUTRITION OF FARM ANIMALS 

of the room are entirely closed, nothing more can be effected 
in this manner toward maintaining its temperature, and if the 
weather continues to grow colder, the fire in the room must be 
increased. Similarly, if the external cooling effect upon the 
animal becomes so great as to exceed the limits of physical ad- 
justment, more fuel material is katabolized, that is, more heat 
is produced. This method of maintaining the body temperature 
is commonly called chemical regulation. 

353. Mechanism of chemical regulation. — The chemical 
regulation is probably effected largely through muscular action, 
by visible motion or by an increase in the muscular tonus, 
either of which involves an increased heat production. This 
has been clearly shown to be true of man and probably applies 
also to other animals. Above the critical temperature, there 
appears to be a slight increase in the heat production with 
rising temperature, probably due to the additional energy ex- 
pended in the various processes of physical regulation. 

354. Critical temperature. — The temperature at which the 
physical regulation gives way to or begins to be supplemented 
by the chemical regulation has been called the critical tempera- 
ture. 1 Above this temperature the radiating capacity of the 
body surface is varied to meet the varying conditions ; below 
it, this method of regulation is largely exhausted and therefore 
the heat production is varied to meet the need. The critical 
temperature for man wearing ordinary clothing appears to be 
about 1 5 C. ; for the dog it is about 20 C, for the guinea pig 
3o°-35°, and for the hog, according to the results of Tangl 2 
and of Von der Heide and Klein, 3 about 2o°-23° C. 

355. Other thermal conditions. — Any conditions tending to facili- 
tate the escape of heat from the body will obviously act like a fall of 
temperature. Wind, for example, by removing the layer of partially 
warmed air next to the skin, tends to remove heat more rapidly from 
the body, so that the cold is felt more severely on a windy day, while, 
on the other hand, the effect of a high temperature is modified by 
wind. A high percentage humidity of the air on a warm day hinders 
the removal of heat by evaporation, so that a moist heat is more try- 
ing than a dry heat. Cold moist air, on the other hand, facilitates 

1 The term refers, of course, to the temperature of the surroundings and not to 
that of the animal itself. 

2 Biochem. Ztschr., 44 (1912), 252. 3 Ibid., 55 (1913), 195. 



THE FASTING KATABOLISM 265 

the escape of heat from the body by increasing the conducting power 
of the clothing, hair or fur, so that a damp cold is more severe than 
a dry cold. The direct rays of the sun may impart a considerable 
amount of heat to the body, thus moderating the effects of low tem- 
peratures and, on the other hand, increasing those of high tempera- 
tures. To be strictly accurate, then, one should speak of a critical 
thermal environment of the animal rather than simply of a critical 
temperature. 

356. Influence on katabolism. — It is apparent from the 
foregoing facts that the energy katabolism of the fasting animal 
is affected by the external temperature and other thermal con- 
ditions to a considerably less extent than *has been frequently 
imagined. It is by no means true that every fall in external 
temperature results in an increased katabolism in the animal 
for the sake of heat production, for if this were the case the con- 
verse would arlso be true, viz., that every rise in the external 
temperature would cause a corresponding decrease in the katab- 
olism, so that finally, when the external temperature was 
equivalent to that of the body, the katabolism would be reduced 
to zero ; that is, we should have life without katabolism, which 
is a contradiction in terms. 

The fact that the heat production of an animal reaches a 
minimum at the critical temperature and that above that point 
it either remains unchanged or increases slightly shows that its 
extent is not determined by the needs of the organism for heat 
as such, since these diminish as the temperature rises. As a 
matter of fact, the production of heat in the body is not the 
purpose of katabolism but merely an incident of it. Heat is 
the form which the chemical energy of the katabolized material 
takes after it has served its purposes in the vital processes, and 
the nearly constant heat production above the critical tem- 
perature is simply due to the fact that the quantity of energy 
required for the internal work of the body is approximately 
constant and cannot be reduced simply by raising the external 
temperature. Heat is essentially an excretum to be gotten rid 
of. Incidentally, in warm-blooded animals, it serves also to 
maintain the body temperature necessary for the normal per- 
formance of the vital functions, but above the critical tempera- 
ture there is a surplus over the amount required for this 
purpose which is disposed of by the processes of physical regu- 



266 NUTRITION OF FARM ANIMALS 

lation already described. It is only when the external tem- 
perature sinks below this point that the katabolic processes 
are stimulated and more heat is produced, and only below this 
point, therefore, does the external temperature influence the 
energy requirement. 

357. Effects of extremes of temperature. — The regulation of 
body temperature described in the foregoing paragraph is possible 
only within certain limits. 

At very low temperatures the possibilities of chemical regulation 
may be exhausted, so that the animal is unable to produce heat as 
fast as it is abstracted and the body temperature begins to fall. An 
actual lowering of the body temperature, however, reduces the inten- 
sity of the katabolism exactly as it does in the case of a cold-blooded 
animal ; the heat production sinks, bringing about a further fall in 
body temperature which again further diminishes the heat production, 
so that the animal speedily perishes from cold. 

At very high temperatures the reverse process may take place. 
When the possibilities of physical regulation are exhausted, the body 
temperature rises. A very slight rise, however, has been shown to 
stimulate the katabolism and therefore the heat production, giving 
rise to a "vicious circle" which is the converse of that occurring at 
very low temperatures and which speedily leads to the animal being 
overcome by heat. 



CHAPTER VIII 
MAINTENANCE — THE ENERGY REQUIREMENTS 

358. Definition of maintenance. — Feed is supplied to farm 
animals either that they may yield products useful to man as 
materials for human food and clothing or that they may serve 
him by the performance of mechanical work. 

But much as a factory must first be supplied with enough 
power to keep in motion the shafting, belting and machinery 
in general before any product can be turned out, so the animal 
mechanism must be provided with sufficient feed to maintain 
the processes essential to life before any continued production 
is possible. The amount required for this purpose is called 
the maintenance ration of the particular animal. It is the 
quantity necessary simply to support the animal when doing 
no work and yielding no material product. A balance experi- 
ment with an animal receiving precisely a maintenance ration 
would reveal an exact equality between income and outgo of 
ash, nitrogen, carbon, hydrogen and energy, showing that the 
body was neither gaining nor losing protein, fat, carbohydrates 
nor mineral elements. From this point of view, maintenance 
might be characterized as a state of labile equilibrium between 
the anabolic and katabolic processes of metabolism (203). 

The word maintenance is sometimes used popularly in an- 
other sense to signify the total amount of feed required, for 
example, by a horse in order to perform his daily work or by a 
calf in order to make a normal growth. It is important to grasp 
the idea that, in its technical sense, the maintenance ration 
means the minimum required simply to maintain life. The 
total feed of the horse or calf would, from this point of view, be 
regarded as consisting of two portions ; one of them the main- 
tenance ration, which if fed by itself would just support the 
horse at rest or the calf without growth, and the other the 
productive portion of the ration, by means of which work is 

267 



268 NUTRITION OF FARM ANIMALS 

done or growth made. To recur to the illustration of the fac- 
tory, the maintenance ration keeps the empty machinery 
running, while the additional feed furnishes the power neces- 
sary to turn out the finished product. 

359. Significance of the maintenance ration in practice. — 
It might seem at first thought that not much importance at- 
taches to a determination of the maintenance ration. The 
animal kept on such a ration yields no direct economic return 
and hence simple maintenance feeding is to be avoided, so far 
as possible, while if it appears desirable to practice it the ob- 
servation of the skilled stockman, especially if supplemented 
by occasional weighings, will usually suffice to determine whether 
or not the end is being attained. Nevertheless, the subject has 
much significance both for practice and for science. 

A very considerable fraction of the feed actually consumed 
by farm animals — on the average probably fully one-half — 
is required simply for maintenance. But if half of the farmer's 
feed bill is expended for maintenance, it is clearly important 
for him to know something of the laws of maintenance, — how 
its requirements vary as between different animals, how they 
are affected by the conditions under which animals are kept, 
how different feeding stuffs compare in value for maintenance, 
etc., — as well as to understand the principles governing the 
production of meat, milk, or work from the other half of his 
feed. 

360. Bearing on interpretation of feeding experiments. — 
From the point of view of the experimenter a knowledge of 
the maintenance requirement is likewise of great importance. 
In any rational study of the laws of nutrition, it is plainly 
inadmissible to attempt to establish general principles by a 
comparison of the feed with one of its effects, viz., production, 
while ignoring entirely its other effect, viz., maintenance. 
Failure to appreciate this fact is responsible for many mislead- 
ing deductions from feeding experiments in the past. 

It has been quite usual to compare the results of such experi- 
ments by computing the ratio of feed consumed to product 
yielded — i.e., either the feed consumed per pound of gain 
made or the gain produced per pound of feed consumed. Such 
a comparison, however, may give an entirely distorted idea of 
the real teachings of an experiment. Suppose, for example, 



MAINTENANCE -THE ENERGY REQUIREMENTS 269 

that in a fattening experiment the quantities of two different 
rations consumed and the gains made were as follows :- 

First Ration Second Ration 

18.0 lb. 21.0 lb. 

Feedeaten i.olb. 1.5 lb- 

Daily gain 

Compared in the way just indicated, the feed required to pro- 
duce one pound of gain was 18 pounds and 14 pounds respectively 
or the second ration appears to have been superior to the first 
bv about 29 per cent. If, however, it was found that in each 
case 12 pounds of the feed were required simply to maintain 
the animal, a very different comparison is obtained, viz. : 

Fikst Second 

Ration Ration 

Lb. Lb. 

18.0 2I-0 

Feedeaten I20 I2 

Expended in maintenance — — 

Surplus left for production i '° ^ 

Daily gain ■■••••• 6.0 6.0 

Surplus feed per pound of gain 

The real value of the two rations per pound is thus shown to 
have been the same. The economic advantage on the side o 
the second was not due to any higher nutritive value but 
simply to the fact that more of it was eaten. Similarly, if the 
oregoing results be supposed to have been obtained, not with 
two different rations but with two different animals on the 
same kind of feed, the experiment does not show that the second 
animal digested or assimilated his feed any more efficiently than 
the first, but simply demonstrates the economic advantage : o 
a larger consumption of feed. It scarcely need be added that 
the same principle applies to all cases of productive feeding as 
has recently been shown in a very striking manner by Eckles 
in experiments upon dairy cows. Clearly, a knowledge of 
the maintenance ration is essential to any logical interpretation 

of experimental results. „„j;„„ tr> 

361. Requirements for maintenance. - Corresponding to 
the dual function of the feed (263) as a source of energy for he 
bodily activities and of specific substances necessary for the 
growth, maintenance and repair of the tissues, the maintenance 

1 Mo. Exp. Sta., Research Bui. No. 2. 



270 NUTRITION OF FARM ANIMALS 

requirements of the animal and the values of feeding stuffs and 
rations for that purpose may be considered from two points of 
view: — 

First, we may inquire how much energy is necessary to sup- 
port the quiescent animal and what amounts of it the various 
feeds and rations can supply in forms available for this purpose. 

Second, we may ask what specific materials and how much 
of each must be supplied in the feed to make good the losses 
due to the continual katabolism of body substances. It is 
particularly the proteins, or rather the amino acids composing 
them, and the ash ingredients and perhaps the so-called vita- 
mines which need to be considered in this respect, the body ap- 
parently possessing large powers of manufacturing other neces- 
sary ingredients from those supplied in ordinary feeding stuffs. 

It will be convenient to consider these two general classes of 
maintenance requirements in the order named, the present 
chapter dealing with the energy requirements. 

362. Mutual replacement of organic nutrients. — The dis- 
cussion$ in Chapter V, of the functions of the principal groups 
of organic nutrients (262-267) showed that, besides certain 
specific values as sources of particular chemical compounds, 
they all serve as carriers of chemical energy for the needs of the 
organism. It would be anticipated, therefore, that the various 
digestible nutrients might mutually replace each other or the 
ingredients of the body, and numerous experiments have shown 
that such is indeed the case. 

Fats fed to a previously fasting animal diminish or suspend 
the loss of body fat, while carbohydrates may be substituted for 
the feed fat with a similar result. As has already been shown 
(337), body protein may replace body fat in the katabolism of 
the fasting animal, while when protein is given to such an ani- 
mal the non-nitrogenous portion of the molecule serves as a 
source of energy to the organism and can be substituted for body 
fat. On the other hand, an excess of feed protein above the 
minimum requirement can be replaced by fats or particularly by 
the carbohydrates, and likewise by organic acids. 

In brief, the animal organism manifests a remarkable degree 
of flexibility as regards the nature of the material which it can 
utilize for its energy metabolism. Aside from the small min- 
imum of protein required, the metabolic activities of the body 



MAINTENANCE — THE ENERGY REQUIREMENTS 271 

may be supported, now at the expense of the stored body fat, 
now by the body protein, and again by the proteins, the fats, 
the carbohydrates, or the organic acids, of the feed. What- 
ever may be true economically, physiologically the welfare of 
the mature animal is not conditioned upon any fixed relation 
between the classes of nutrients in its feed supply, apart from the 
minimum requirements for protein and ash. But while the 
body may draw its energy from the most varied feed materials, 
it by no means follows that the gross energy of these materials 
is of equal value for the functions of the organism. On the 
contrary it has been shown that there are wide differences in this 
respect. 

§ 1. Net Energy Values for Maintenance 

363. Method of determination. — The value of any nutrient 
or feeding stuff as a source of energy for maintenance is obviously 
measured by the extent to which it can diminish the loss of 
energy which the body would otherwise suffer. Suppose, for 
example, that a fasting dog was found to produce 600 Cals. 
of heat per day by the katabolism of his own tissues. If, in a 
subsequent experiment, fat be fed, this loss from the body will 
be diminished, more or less feed fat being virtually katabolized 
in place of body tissue. If fifty grams of fat are fed, and if a 
balance experiment shows that the loss of energy from the 
body is reduced from 600 Cals. to 200 Cals., it is plain that 
each gram of fat has reduced the loss by 400 -s- 50 = 8 Cals. 
and the latter number shows the value of this particular fat 
for the maintenance of this particular animal. 

364. Comparison with metabolizable energy. — As already 
defined (322), metabolizable. energy is that portion of the 
gross energy of the feed which is not carried off as chemical 
energy in the excreta but is capable of transformation in the 
body. It was natural to suppose, therefore, that the metab- 
olizable energy of a substance would represent its value for 
maintenance and this was long believed to be true, but later 
investigations have shown that such is not the case. 

For example, in balance experiments by Armsby and Fries a 
steer received in successive periods two different amounts of 
timothy hay, both insufficient for maintenance. The metab- 



272 



NUTRITION OF FARM ANIMALS 



olizable energy of the hay and the heat production per day, 
determined in the manner illustrated in Chapter VI (322, 329), 
were as follows : — 



Table 37. — Determination of Net Energy Value of Timothy Hay 



Period 4 

Period 3 

Difference 

Difference per lb. dry matter of 
hay 



Dry Mat- 
ter of 
Hay Eaten 



Pounds 

10.21 
6.17 



4.04 



Metabo- 

LIZABLE 

Energy 



Cals. 

9544 
5768 



3776 
935 



Heat Pro- 
duced 



Cals. 

9812 
8064 



1748 
433 



Gain of 
Energy l 



Cals. 

- 268 
-2296 



2028 



502 



The 4.04 pounds of hay (water-free), added to the insufficient 
ration of Period III diminished the loss of energy from the 
body of the animal by 2028 Cals. ; that is, they contributed 
this amount towards its maintenance. The net effect of the 
hay, therefore, computed exactly as in the supposed case of 
the dog in the preceding paragraph, was 2028 -s- 4.04 = 502 
Cals. per pound of dry matter. But the added hay contained 
metabolizable energy to the amount of 935 Cals. per pound of 
dry matter. Clearly, therefore, by no means all of the metab- 
olizable energy of the hay could be utilized for maintenance 
by the steer. Only 502 Cals. were used for this purpose, in 
place of energy previously derived from the katabolism of 
the fat and protein of the body, while the remaining 433 Cals. 
were, indeed, metabolized in the body, but resulted simply in 
increasing the heat production by this amount. 2 The propor- 
tion of the metabolizable energy of this hay which was available 
for maintenance, then, was 502 -r 935 =53-7%- The fore- 
going result is typical of a large number of others which have 
been reached in experiments on various species of animals. 

1 Since submaintenance rations were fed, the gains were of course negative, 
i.e., chemical energy was lost from the body. 

2 Since gains of energy are computed from the difference between income and 
outgo, the figures of the last column of the table necessarily agree with those of the 
two preceding ones. They simply present a different aspect of the same facts. 






MAINTENANCE — THE ENERGY REQUIREMENTS 273 

Even in the case of pure, or nearly pure, nutrients fed to carniv- 
ora, their maintenance values are less than their content of 
metabolizable energy. 

365. Feed consumption increases heat production. — From 
a slightly different point of view, the experiment just cited 
furnishes a good illustration of the important fact that the 
consumption of feed tends to increase the heat production of 
the body. This is an observation as old as the time of Lavoi- 
sier. That investigator observed the oxygen consumption of 
a man to increase materially (about 37 per cent) after a meal, 
and a multitude of subsequent experiments by numerous in- 
vestigators and on various species of animals have fully con- 
firmed these earlier results, so that the fact of an increased metab- 
olism consequent on the ingestion of feed is fully established. 
It is especially to the investigations of Zuntz and his associates l 
that the demonstration of this fact and the recognition of its 
significance in relation to the nutritive values of feeding stuffs 
is due. 

For example, Zuntz and Hageman, 2 on the average of a number of 
experiments in which the respiratory exchange of a horse shortly 
before feeding in the morning, shortly after feeding, and some hours 
later was determined by means of the Zuntz form of the Pettenkofer 
apparatus (299), obtained the following results, computed per kilo- 
gram live weight per minute. 

Table 38. — Heat Production by a Horse 



Fasting 

23 minutes after feeding 
3^ hours after feeding . 



Oxygen 
Consumed 



Cubic 
Centimeters 

3-339 
3.648 

3-704 



Computed 
Heat Pro- 
duction 



Gram-calories 

16.929 

18.510 
18.787 



The same effect has been invariably observed with cattle in experi- 
ments by Armsby and Fries 3 in which the heat production was deter- 
mined directly by means of the respiration calorimeter. Thus in an 

1 Compare the writer's Principles of Animal Nutrition, pp. 377 _ 385- 
2 Landw. Jahrb., 27 (1898), Erganzbd. Ill, 282. 
3 Jour. Agr. Research, 3 (1915), 435. 
T 



274 



NUTRITION OF FARM ANIMALS 



experiment in which three different amounts of alfalfa hay were fed 
to the same steer in different periods the results were as follows : — 

Table 39. — Heat Production by a Steer 



Period 1 
Period 3 
Period 5 



Dry Matter 

of Feed per 

Day 




Heat Pro- 
duced per 
Day 



Cals. 

11272 

10388 

7754 



Kellner's respiration experiments on fattening cattle have shown 
that the same effect is produced when feed is added to a basal ration. 
Thus when wheat gluten was added to a light fattening ration 1 the 
heat production as calculated (329) from the balance of matter was 
as follows : 

Table 40. — Heat Production by an Ox 



Period 1, Basal ration 
Period 4, Same + gluten 



Dry Matter 

of Feed per 

Day 




Heat Pro- 
duced per 
Day 



Cals. 

I934I 

24007 



For many years it was taught, in accordance with Rubner's theory 
of "isodynamic replacement," that with carnivora, and presumably 
with man, the nutrients were of value in proportion to their content 
of metabolizable energy. Rubner's own later investigations, 2 how- 
ever, as well as still more recent ones by Lusk and his associates 
(367 e), have shown that what is true of the feeding stuffs consumed by 
horses and cattle is also true of nearly pure nutrients fed to dogs, viz., 
that if the experiment be made above the critical temperature for the 
animal there is in each case an increase in the heat production, so that 
the metabolizable energy is only partially available for maintenance. 
Thus the average of two of Rubner's experiments in which lean meat 
was fed gave the following results as compared with the fasting state : 



1 Landw. Vers. Stat., 53 (1900), 130-131. 

2 Die Gesetze des Energieverbrauchs bei der Ernahrung, 1902. 



MAINTENANCE — THE ENERGY REQUIREMENTS 275 
Table 41. — Heat Production by a Dog 



Fasting 
Fed . 




Daily Heat 
Production 
per Kilo- 
gram Live 
Weight 

Cals. 

5I-50 

70.55 



Proteins are especially efficient in stimulating the heat production but 
fats and carbohydrates produce the same effect although to a much 
less degree. 

366. The specific dynamic action. — The effect of the various 
nutrients, notably of protein, in raising the heat production of 
the animal above the fasting level, as in the experiments just 
cited, has been called by Rubner their specific dynamic action. 
Kellner 1 has proposed a different terminology. He divides 
the metabolizable energy of the feed into thermic and dynamic 
energy. Thermic energy, equivalent to Rubner's specific 
dynamic action, signifies that portion of the metabolizable 
energy which is of value to the organism only as a source 
of heat. Dynamic energy, equivalent to net energy as defined 
in a subsequent paragraph (370), on the other hand, is that 
portion of the metabolizable energy which can be utilized for 
the performance of the vital functions. 

367. Causes of increased heat production. — The consump- 
tion of feed sets in operation (or increases) a variety of activities 
not manifested by the fasting organism. 

a. Mechanical Work. — A not inconsiderable amount of 
muscular activity is expended by farm animals and especially 
by the herbivora in the prehension and mastication of their 
feed and in moving it through the alimentary canal. Since 
muscular work involves an expenditure of energy, all of which, 
in the case of internal work, finally takes the form of heat (342), 
the mechanical work of digestion is a considerable factor in 
increasing the metabolism of farm animals, although Armsby 
and Fries 2 have presented reasons for believing that peristalsis 

1 Ernahrung landw. Nutzt., 6th Ed., p. 105. 

2 Jour. Agr. Research, 3 (1915), 479. 



276 NUTRITION OF FARM ANIMALS 

in cattle does not contribute very largely to the increased heat 
production consequent on the consumption of feed. 

b. Glandular activity. — The increased metabolism required 
for the secretion of the digestive fluids and for the excretion of 
metabolic products is also to be reckoned among the causes of 
the heat production consequent on the ingestion of feed. 

c. Fermentations. — The extensive fermentations, especially 
the methane fermentation, occurring in the digestive tract of 
herbivora (128-130, 132) result in a considerable evolution of 
heat. No entirely satisfactory determinations of its amount 
have yet been reported, but Von der Heide, Klein and Zuntz * 
compute from Markoff's experiments that the methane fer- 
mentation in cattle gives rise to the evolution of 4.374 Cals. of 
heat per cubic centimeter of methane, equivalent to 6.07 Cals. 
per gram. 

d. Intermediary metabolism. — The chemical changes which 
the nutrients undergo during digestion and resorption and 
especially in the intermediary metabolism (compare Chapters 
III and V) have been invoked to explain the increased heat 
production consequent on the consumption of feed, particularly 
of protein, but apparently without sufficient warrant, most 
of these reactions seeming to be substantially isothermic. 

e. Direct stimulus to metabolism. — Recent investigations by 
Lusk and his associates 2 upon the cause of the specific dy- 
namic action, together with earlier experiments by Gigon, 3 
have gone far towards clearing up the subject. According to 
Lusk, the action of carbohydrates and fats is to be explained 
substantially as was done by C. Voit in 1881, viz., as the direct 
effect of a greater supply of non-nitrogenous material to the 
cells, i.e., as virtually a case of mass action. The products of 
protein katabolism, on the contrary, particularly the hydroxy 
and keto-acids resulting from the deaminization of the amino 
acids (233), act as direct stimuli to the katabolism of non- 
nitrogenous matter in the body cells. 

That these actions play their part, along with mechanical 
work and fermentations, in bringing about the increased heat 

1 Landw. Jahrb., 44 (1913). 795- 

2 Jour. Biol. Chem., 12 (1012), 349; 13 (1912), 27, 155, 185; 20 (1915), 555- 
Proc. Internat. Cong. Hygiene, 1913. Arch. Inter. Medicine, 12 (1913), 485. Jour. 
Amer. Med. Asso., 63 (1914), 824. 

3 Skand. Arch. Physiol, 21 (1909), 35* ; Arch. Physiol. (Pfliiger), 140 (191 1), 548. 



MAINTENANCE — THE ENERGY REQUIREMENTS 277 

production resulting from the consumption of feed by herbivora 
cannot be doubted. Besides proteins, carbohydrates and fats, 
however, the feed of herbivora contains a great variety of other 
substances and the results upon steers obtained by Armsby and 
Fries x seem to indicate that among these there may be com- 
pounds acting specifically as stimuli to the cell metabolism or 
to the minor muscular movements of the animal. Among the 
feeding stuffs examined, this appeared to be notably true of 
alfalfa hay and maize meal. 

368. " Work of digestion." — The expenditure of energy 
by the body which results from the ingestion of feed has been 
somewhat loosely, and perhaps not altogether fortunately, 
designated as " work of digestion." While there may be ob- 
jections to the term and while it must not be interpreted too 
literally, it may nevertheless serve a useful purpose as a col- 
lective expression for the energy cost to the organism of all the 
various processes involved in the digestion and assimilation of 
the feed. Its total amount is equal, of course, to the extra 
heat produced above that generated by the fasting animal. 
Rubner's specific dynamic action, or Kellner's thermal energy, 
is equivalent to the " work of digestion " in this broad mean- 
ing. The considerations presented in the previous paragraphs 
serve to indicate some of the factors of the " work of digestion " 
and render it evident that it is by no means all work in the 
mechanical sense. In herbivora this factor is an important 
one, while with man and carnivora it apparently plays a small 
part. A similar difference is strikingly shown in the case of the 
digestive fermentations, which are very extensive in ruminants 
but play a subordinate role in other animals. 

369. Significance of expenditure of energy in feed con- 
sumption. — Whatever the part played by various factors in 
the increase of metabolism due to feed ingestion, the existence 
of that increase and the consequent augmented heat production 
is a fully established fact which has an important bearing upon 
the value of the feed as a source of energy. 

Recurring once more to the comparison of the animal body 

with an internal combustion motor (274), if a gasoline engine 

has to obtain its supply of fuel by hoisting it from a lower' 

level, it is evident that the energy spent in this way diminishes 

1 Jour. Agr. Research, 3 (1915), 479. 



278 NUTRITION OF FARM ANIMALS 

to just that extent the quantity of energy which the engine 
can deliver in other forms of work, so that the effect is 
virtually the same as if the energy content of the gasoline 
as delivered at the cylinder were diminished by the same 
amount. 

In a precisely similar way, the energy expended in the so-called 
" work of digestion " and eliminated as heat does not serve the 
general purposes of the body. It cannot be said to be waste 
energy, like the chemical energy of the feces, for example, since 
part at least is expended for necessary purposes. The feed must 
be eaten and assimilated, just as the gasoline for the engine must 
be hoisted. The energy spent in so doing, however, consti- 
tutes virtually a deduction which must be made from the meta- 
bolizable energy of the feed in order to obtain the net amount 
of energy which it can contribute to the performance of the 
necessary internal work of the body (i.e., to its maintenance) 
or to such processes as the performance of external work or the 
storage of meat or fat. 

370. Net energy values. — By means of balance experiments 
like that with a steer used as an illustration in a previous para- 
graph (364), the effect of a feeding stuff upon the heat produc- 
tion of an animal or the amount of energy which it contributes 
towards the maintenance of the body may be determined. 
The latter result has been called the net energy value of the sub- 
stance because it shows the net result as regards energy obtained 
by its use. The net energy value of the hay in the illustration 
cited was 502 Cals. per pound of dry matter. Net energy might 
be defined, therefore, as metabolizable energy minus the work of 
digestion, the latter term, of course, being understood in the 
very general sense already indicated as equivalent to the 
additional heat production caused by the consumption of 
the feed. 

Stated in a slightly different way, the net energy value of a 
feeding stuff is the energy remaining after the losses of chemical 
energy in the various excreta and also the energy expended in 
the processes incident to the consumption of the material 
have been deducted from its gross energy. The amount of these 
deductions naturally varies as between different feeding stuffs. 
One containing much digestible matter, readily masticated and 
exerting little stimulating effect on the metabolic processes 



MAINTENANCE -THE ENERGY REQUIREMENTS 279 

(367 c), that is, causing little " work of digestion," will have a 
relatively high net energy value; while, on the other hand, 
materials of low digestibility, which undergo extensive fer- 
mentations, require much muscular work in their mastication 
and digestion, or stimulate the body metabolism, will have 
correspondingly low net energy values. 

371 Net energy values for different purposes. — I be net 
energy value of the same feeding stuff may differ according to 
the species of animal by which it is consumed and the purpose 

for which it is used. 

The structure of the digestive organs of different species varies 
and, as is shown in Chapter XVI (713-717), specific differences 
in digestive capacity exist. In other words the proportion of 
the gross energy of a feeding stuff which is lost in the feces 
differs as between different species, and therefore its net energy 
value tends to vary accordingly. Similarly, the extent to which 
bacterial fermentations occur in the digestive tract of an animal 
tends to influence the net energy value of its feed m two ways 
The more extensive these fermentations, the less of the chemical 
energy of the feed is rejected in the feces but, on the other hand, 
the more chemical energy is given off in the combustible gases 
excreted or is transformed into heat in the process of fermenta- 
tion and increases the " work of digestion." Finally, it appears 
not unlikely that the mechanical work required in mastication 
and digestion may vary as between different species. _ 

The materials resorbed from maintenance or submaintenance 
rations may be regarded chiefly as fuel to be oxidized more or 
less directly, while in the fattening or growing animal a part ot 
the digested nutrients is transformed into flesh or fat, or in 
the milking animal into butter fat, lactose, casein etc. lhe 
net energy values for these purposes would evidently be equal 
to the amounts of energy contained in the gains made and 
might very well differ from the values for simple maintenance. 
The net energy values of feeding stuffs for different species 
and for the various purposes for which farm animals are kept, 
together with the methods for their determination or estimation, 
are discussed in Chapter XVII and the average results for a 
considerable number of feeding stuffs are tabulated in the Ap- 
pendix. What is essential at this point is to acquire a clear 
idea of the general conception. 



280 NUTRITION OF FARM ANIMALS 

§ 2. The Maintenance Requirements of Farm Animals 

372. True maintenance and live weight maintenance. — 

The maintenance of an animal in the strict sense signifies the 
preservation of the store of matter and of potential energy 
contained in the body, and only a ration which effects this is 
really a maintenance ration. As will appear in subsequent 
pages, however, much of the recorded information regarding 
the maintenance ration is derived from experiments in which 
the criterion of the sufficiency of the ration was its effect in 
maintaining the live weight of the animal. In experiments on 
mature animals and extending over a considerable period of 
time, it is unlikely that any gross error is involved, especially 
if determinations of the nitrogen balance show the protein 
supply to be adequate. In short periods, on the other hand, 
and especially in experiments on young animals, the live weight 
is a notoriously untrustworthy guide. The general reasons 
for this are familiar, but in young animals another very impor- 
tant factor enters into consideration. As is well known, the 
tendency to growth is one of the most marked characteristics 
of young animals. Waters x has shown that this impulse to 
increase of tissue is so marked that it may apparently take pre- 
cedence over the demand for maintenance, and that an animal 
may even maintain its weight and continue to increase in size 
of skeleton for a considerable time on a sub-maintenance ration. 

Some 15 immature cattle were fed for considerable periods on 
rations just sufficient to maintain their live weight. Under these 
conditions, the animals continued to grow in height, in depth of chest 
and length of head. At the same time, however, there was" an evi- 
dent falling off in the amount of fat tissue, both as judged by the eye 
and as shown by the appearance and by the chemical composition of 
the carcass. Histological studies, too, showed a reduction in the size 
of the fat cells and analyses of the adipose tissue showed a lower fat 
and higher water and protein content than in check animals. What 
occurred was evidently a consumption of body fat to supply energy, 
while at the same time an approximately equal weight of protein 
tissue was produced, which, on account of the relatively low energy 
value of protein and of the relatively large amount of water accom- 
panying it, represented a much smaller quantity of energy than did 
the fat tissue which disappeared. In other words the rations were 

1 Soc. Prom. Agr. Sci., Proc. 29th Annual Meeting (1908), p. 71. 



MAINTENANCE — THE ENERGY REQUIREMENTS 281 

not really but only apparently maintenance rations. It is perhaps 
hardly correct to say that in these experiments growth was main- 
tained at the expense of the fat of the tissues. A more exact state- 
ment of the case would be that the increase of protein tissue and 
water masked the loss of fat. Presumably this effect would be less 
marked in more mature animals, in which the true maintenance and 
the live weight maintenance would doubtless approach each other 
closely when measured over long periods. 

373. Methods of determining the maintenance requirement. 

— The most obvious method for determining the maintenance 
requirement of an animal is the method of trial. It consists of 
varying the amount of feed until constancy of live weight is 
attained or until a balance experiment shows equilibrium be- 
tween income and outgo of matter and energy. This method, 
if extended over a considerable length of time, is particularly 
adapted to the determination of the live weight maintenance. 
When tested by the more refined method of the balance ex- 
periment, however, such a ration will only rarely and by acci- 
dent be found to be exactly a true maintenance ration. Usu- 
ally there will be revealed more or less gain or loss by the body 
for which a correction must be applied. 

A second method consists of a comparison, like that used in 
a previous paragraph (364), to illustrate the determination of 
net energy values, between the effects of two different amounts 
of the same feeding stuff or ration upon the balance of energy. 
Such a comparison not only affords the means of computing 
the net energy value of the feed consumed but also serves to 
determine the energy requirement of the animal. The results 
in the case cited were as follows : — 

Table 42. — Determination of Maintenance Requirement 



Period 4 

Period 3 

Difference 

Difference per lb. of dry matter of hay 



Dry 

Matter 
of Hay 
Eaten 



Pounds 

10.21 
6.17 



4.04 



Metab- 
olizable 
Energy 



Cals. 

9544 
5768 



3776 
935 



Heat 
Pro- 
duced 



Cals. 
9812 
8064 



1748 
433 



Gain of 

Energy 



Cals. 

-268 
-2296 



2028 
502 



282 NUTRITION OF FARM ANIMALS 

Each pound of dry matter of the hay decreased the loss of energy 
from the body by 502 Cals. The ration of 10.21 lb. still 
permitted a loss from the animal of 268 Cals. To reduce this 
loss to zero would obviously require the addition of 268 -r 502 
= 0.53 lb. and an exact maintenance ration as regards energy 
would have been 10.21 + 0.53 = 10.74 pounds of the hay. 
In precisely similar fashion the metabolizable energy required 
for maintenance was 

9544 + 268 X -f-g-Jf = 10042 Cal. 

374. Computation of the fasting katabolism. — Another 
method of comparison, however, is of greater significance, since it 
affords results of more general value and also serves to bring out 
clearly the relations between the net energy values of feeding 
stuffs, the fasting katabolism and the maintenance requirement. 

In the foregoing experiments each pound of hay withdrawn 
from the ration caused the heat production to decrease by 
433 Cals. If, then, all the hay were withdrawn from Period 3 
and the animal reduced to the fasting state, the heat production, 
or in other words the fasting katabolism, would be 

8064 - (433 X 6.17) = 5392 Cals. 

The same result may also be computed from the losses of 
energy suffered by the animal. The withdrawal of each pound 
of hay increased this loss by 502 Cals. The withdrawal 
of all the 6.17 pounds of Period 3, therefore, would increase 
the loss by 502 X 6.17 = 3096 Cals., making a total loss 
of 5392 Cals., equal to the fasting katabolism. In other 
words, by such a comparison as the foregoing it is possible to 
determine indirectly the fasting katabolism, which it is scarcely 
practicable to determine directly. 

It was shown in Chapter VII (344), however, that the fast- 
ing katabolism is the measure of the maintenance requirement. 
To maintain the steer of this illustration it would be necessary 
to supply in his feed an amount of energy, after deducting the 
losses in the excreta (i.e., an amount of metabolizable energy), 
equal to the fasting katabolism, 5372 Cals., plus a sufficient 
additional amount to offset the additional heat production 
which the consumption of the feed would inevitably occasion, 
i.e., the work of digestion. 



MAINTENANCE — THE ENERGY REQUIREMENTS 283 

But the difference between the metabolizable energy and 
the work of digestion is the net energy (370). Consequently 
the foregoing statement is equivalent to saying that the main- 
tenance requirement of the steer was 5392 Cals. of net energy. 
Each pound of this particular hay had a net energy value of 
502 Cals. To maintain the animal, therefore, there would be 
required 5392 -5- 502 = 10.74 lb., as previously computed. 

375. Manner of stating the maintenance requirement. — 
Evidently the maintenance requirement of an animal, such as 
the steer of the foregoing illustration, may be stated in a va- 
riety of ways — in terms of weight of feed, of amounts of di- 
gestible nutrients, of metabolizable energy or of net energy. 
So far as the results of a single experiment are concerned, it 
makes little difference which manner of statement is adopted, 
since they are all simply different ways of expressing the same 
facts. When it is desired to make general statements, however, 
there are very manifest advantages in stating the maintenance 
ration in terms of net energy. 

It was shown in Chapter VII (343) that the fasting katabo- 
lism might be regarded as practically constant under uniform 
conditions. Consequently the net energy requirement for 
maintenance is equally constant, and in the foregoing example 
any ration having a net energy value of 5392 Cals. would 
have been a maintenance ration. 

But since the net energy values of different feeding stuffs, 
as well as the proportion of their metabolizable energy which 
can be utilized for maintenance, may vary through a consider- 
able range, the weight of feed or the amount of metabolizable 
energy which will suffice to maintain an animal will vary with 
the kind of material fed. For example, it is shown in subsequent 
paragraphs (380, 381) that a thousand-pound steer requires 
about 6.0 Therms of net energy for maintenance. From the 
results of Armsby and Fries' determinations of net energy values 
(760), it is easy to compute that to supply this amount in tim- 
othy hay with a net energy value of 48.63 Therms per 100 
pounds of dry matter would require 6.0 -f- 0.4863 = 12.34 
pounds of dry matter, but that if mixed hay with a net energy 
value of 43.37 Therms per 1000 pounds were used, the amount of 
dry matter necessary would be 6.0 -f- 0.4337 = 13.83 pounds. 
The quantities of metabolizable energy contained in these main- 



284 



NUTRITION OF FARM ANIMALS 



tenance rations would likewise be different, as is shown in the 
following statement, in which are included for further illustra- 
tion two mixed rations used by the same experimenters. 

Table 43. — Examples of Maintenance Rations for a iooo-Pound 

Steer 



Material 



Timothy hay 

Mixed hay 

Corn meal and mixed hay, 2 : 1 
Mixed grain and alfalfa hay, 2 : 1 



Weight 


Metab- 


of Dry 


OLIZABLE 


Matter 


Energy 


Pounds 


Therms 


12.34 


10.38 


13-83 


12.01 


8.68 


11. 11 


9.07 


10.69 



Net 
Energy 



Therms 

6.0 
6.0 
6.0 
6.0 



By stating the maintenance requirement in terms of net energy 
a single value is obtained for an animal, or a single average for 
a class of animals, which is a general expression of its main- 
tenance requirement irrespective (substantially) of the par- 
ticular feed or feeds which may be used to satisfy it, while a 
statement in terms of metabolizable energy or of weight of 
feed must also specify the particular kind of feed to which it 
applies. The greater convenience of the former method for 
the computation of actual rations is evident. To the extent to 
which the net energy values of feeding stuffs are known or can 
be estimated it is possible to make up an almost endless variety 
of combinations which will all be maintenance rations, i.e., 
will furnish the amount of net energy required by the animal. 

In the following paragraphs, this method of expression will be 
followed so far as practicable, although unfortunately compara- 
tively few determinations of the net energy requirements for 
maintenance have yet been reported except in the case of cattle. 

376. Modified conception of energy requirement. — A study 
of the conditions, especially as regards muscular work, which 
influence the katabolism of the fasting animal makes it evident 
that the conception of the energy requirement outlined in 
Chapter VII requires some modification in its application to 
the actual feeding of animals. 

As was there shown (344), the heat production of the fasting 
animal in a state of absolute muscular rest may be regarded as 



MAINTENANCE — THE ENERGY REQUIREMENTS 285 

measuring the quantity of energy indispensable for its internal 
work. As a matter of fact, however, absolute muscular rest 
cannot be maintained for any considerable length of time, at 
least during the waking hours, even by voluntary effort. The 
horse or ox when at rest in the ordinary sense, i.e., when doing 
no external work, is still expending a not inconsiderable amount 
of energy in muscular activities of various sorts, some of which 
were indicated in §3 of the same chapter (348). In particular, 
it was stated (349) that standing as compared with lying causes 
a very marked increase in the heat production, especially in 
the case of cattle. When, therefore, the heat production of 
such an animal in the fasting state is taken as a measure of the 
energy required for its maintenance, it does not represent a 
state of absolute rest but simply with one of relatively less 
activity. The energy requirement for maintenance in the 
economic sense includes not only the absolute minimum re- 
quired for the internal work but also the amount expended in 
various forms of incidental muscular work which are in a sense 
unnecessary physiologically but are unavoidable practically. 
Moreover, since the amount of this incidental work is more or 
less variable as between different individuals and in the same 
individual at different times, the energy requirement for main- 
tenance is not a fixed, constant quantity whose exact value can 
be determined, but a variable one. The purpose of investiga- 
tion is to show the range of variation which may be expected 
and to determine a general average value for the conditions of 
ordinary practice. 

The maintenance requirement of swine 

377. Net energy requirement. — With animals such as man, 
carnivora or swine, having a comparatively simple digestive 
apparatus and consuming relatively concentrated feed, the 
fasting energy expenditure can be determined without special 
difficulty by depriving the resting animal of feed during a rela- 
tively short period and measuring the katabolism with the 
aid of a respiration apparatus or calorimeter. The total 
amount of heat produced, determined either directly or 
by calculation, furnishes the measure of the energy expenditure 
and therefore of the net energy requirement for maintenance. 



286 



NUTRITION OF FARM ANIMALS 



Such an experiment must, of course, be made at a temperature 
above the critical temperature (354) for the animal, since other- 
wise the heat produced would be greater than that correspond- 
ing to the necessary internal work by the additional amount 
necessary to maintain the body temperature. 

Numerous determinations of the fasting katabolism of man 
and of the smaller animals, such as the dog, cat, rabbit, guinea 
pig, etc., are on record, but the only experiments of this sort 
upon farm animals are those of Meissl, Strohmer and Lorenz l 
and of Tangl 2 upon swine. 

Meissl's determinations were made at about 20 C, a tern- * 
perature which, according to Tangl's later results, is well above 
the critical temperature for mature swine. In Tangl's experi- 
ments the animals spent most of the time lying; in Meissl's 
paper no statements are made on this point. 

Excluding those of Tangl's experiments which were appar- 
ently below the critical temperature, the results, computed 
per too pounds in proportion to the two-thirds power of the 
live weight, were as follows : — 

Table 44. — Net Energy for Maintenance of Swine 



MeissVs experiments. 

Swine H 1 

Swine H 2 , 

Average , 

TangVs experiments. 
Two mature animals 

at i6°-i7° C 

at 22 C . 

Two growing animals 

at 20 C 

at 23 C 

at26°C 

Average 




Net Energy 
per 100 Pounds 
Live Weight 
per Day 



Therms 
1.283 
1.244 



I.266 



I.220 
I.224 



I.307 
1.226 
I.270 



1.249 



1 Ztschr. Biol., 22 (1886), 63. 



2 Biochem. Ztschr., 44 (191 2), 252. 



MAINTENANCE — THE ENERGY REQUIREMENTS 287 

From the foregoing results it appears that the average daily 
energy expenditure of fasting swine at rest and above the critical 
temperature is about 1.25 Therms per 100 pounds live weight, 
and consequently that a maintenance ration must supply this 
amount of net energy. Assuming a value of 9.02 for the con- 
stant k of Meeh's formula (346), this average is equivalent to 
1.089 Therms per square meter of body surface. Using an 
entirely different experimental method, Fingerling, Kohler and 
Reinhardt l have computed the average energy requirement 
for maintenance of two growing pigs at almost the same 
amount, viz., 1.045 Therms per square meter. 

378. Metabolizable energy in maintenance rations. Un- 
fortunately, few determinations of the net energy values of 
feeding stuffs for swine have been reported (761) and most of 
the data regarding the maintenance requirement of this species 
are expressed in terms of digestible matter or of computed 
metabolizable energy. The metabolizable energy contained 
in actual maintenance rations of swine has been determined in 
a single respiration experiment by Von der Heide and Klein 2 
and may be estimated more or less accurately in a number of 
live weight experiments. Such experiments have been re- 
ported by Taylor, 3 Carlyle, 4 Ostertag and Zuntz 5 and Dietrich. 6 
The results show a very wide range, from a minimum of 0.897 
Therm per 100 pounds live weight for 50-pound pigs on a 
ration of one part meal and 4 parts skim milk to a maximum 
of 2.558 Therms for 100-pound pigs on a ration of shorts, 
corn meal and oil meal. For this there may be a variety of 
reasons. Live weight results are notoriously uncertain (281- 
283), and in growing animals especially the possibility of a main- 
tenance of live weight by a substitution of water for fat (372) 
has to be borne in mind. The feeds used, too, were varied, 
and there seem to be indications that, in some cases at least, 
a smaller " work of digestion," especially in the case of rations 
containing much milk, may have contributed to reduce the 
amount of metabolizable energy necessary for maintenance. 

The averages computed from all the experiments and those ob- 
tained by the omission of a few extreme results are as follows : — 

1 Landw. Vers. Stat., 84 (1914), 149. 2 Biochem. Ztschr., 55 (1913), 195. 

3 Wis. Expt. Sta., Rpt. 1901, p. 67. A Ibid., Bui. 104 (1903), p. 31. 

6 Landw. Jahrb., 37 (1908), 226. 6 Ills. Expt. Sta., Bui. 163 (1913). 



288 NUTRITION OF FARM ANIMALS 

Table 45. — Daily Maintenance Rations of Swine 

Metabolizable energy per 100 lb. live weight 

Maximum 2.558 Therms 

Minimum 0.897 Therm 

Average of all 1-534 Therms 

Average omitting lowest and highest . . . 1.5 10 Therms 

Average omitting lowest and two highest . . 1.474 Therms 

379. Comparison with net energy. — On the average of all 
the respiration experiments on fattening swine which are re- 
corded in Chapter XVII (761), 78.14 per cent of the metab- 
olizable energy supplied may be computed to have been uti- 
lized for maintenance plus gain. If this may be assumed to 
represent approximately the percentage of the metabolizable 
energy available for maintenance, the foregoing maintenance 
rations contained, per 100 pounds live weight, the following 
amounts of net energy : — 

Table 46. — Daily Maintenance Rations of Swine 

Computed net energy per 100 lb. live weight 

Minimum 0.701 Therm 

Maximum 1.998 Therms 

Average of all i- x 99 Therms 

The averarge requirement of net energy as thus computed 
does not differ greatly from the amount indicated by the ex- 
periments on fasting animals (377), but the enormous range in 
the results of the single experiments shows in a striking manner 
the need for further investigation. 

The maintenance requirement of cattle 

380. Net energy requirement. — In the case of ruminants, 
it is hardly practicable to determine directly the net energy re- 
quirement by measuring the katabolism of the fasting animal. 
Prolonged fasting would be required to free the voluminous 
and complicated digestive organs of these animals from feed 
residues, ff this could be accomplished at all, and it would be 
difficult to determine when that point was reached, while it is 
questionable whether the results on such an animal could be 
regarded as normal. 



MAINTENANCE — THE ENERGY REQUIREMENTS 289 

Table 47. — Net Energy Requirement for Maintenance of Cattle 
Corrected to 12 hours standing 



Year 



1902 

1903 
1904 
1905 
1905 
1906 
1906 
1907 
1907 



1908 



1909 



1911 



1912 j 

Average of all ....... 

Average, omitting alfalfa meal . 
Average of expts. with roughage 

only x 

Average of expts. with mixed 

rations . 







Net 






Energy 


Animal 


Kind of Feed 


per Day 

AND IOOO 

lb. Live 
Weight 






Therms 


I 


Timothy hay and a 






little linseed meal 


7-430 


I 


Clover hay 


5.877 


I 


Clover hay 


7.109 


A 


Timothy hay 


5.873 


B 


Timothy hay 


6.052 


A 


Timothy hay 


6.272 


B 


Timothy hay 


6.305 


A 


Timothy hay 


4.723 


B 


Timothy hay 


6.067 


D 


Alfalfa hay 


4.917 


E 


Alfalfa hay 


4.824 


E 


Alfalfa hay and 






grain mixture 


6.295 


C (Fat) 


Alfalfa hay 


5.246 


C (Fat) 


Alfalfa hay and 






grain mixture 


6.099 


F 


Alfalfa hay 


5448 


F 


Alfalfa hay and 






grain mixture 


6-474 


D 


Maize stover 


5.858 


D 


Mixed clover and 






timothy hay 


6.644 


D 


Mixed hay and 






hominy feed 


5.960 


G 


Mixed clover and 






timothy hay 


6-559 


G 


Mixed hay and 






maize meal 


6.141 


H 


Alfalfa hay 


5-7IO 


H 


Alfalfa meal 


3-976 
5.906 
5-995 

5.936 

6.194 



Omitting experiment on alfalfa meal. 



U 



290 NUTRITION OF FARM ANIMALS 

The fasting katabolism of such an animal may, however, 
be computed in the manner already described (374) from a 
comparison of two periods on different amounts of the same 
feed, or ration, both being less than that necessary for main- 
tenance. Twenty-three experiments of this sort, on nine 
different steers, only one of which was fat, in which the rela- 
tive metabolism of the animals when standing and when lying 
was determined, have been made by Armsby and Fries. 1 Com- 
puted per iooo lb., in proportion to the two- thirds power of 
the live weight (347) and corrected 2 to a uniform period of 12 
hours standing out of the 24, the net energy requirements were 
as shown in Table 47. No other experiments on precisely this 
plan have yet been reported. 

Even if a few seemingly extreme results, like those of 1902 
and 191 2 be excluded, the figures show a wide range. The 
trials with mixed rations of roughage and concentrates show 
on the whole somewhat higher results than those with rough- 
age only, but the experiments are hardly numerous enough to 
show whether this difference is significant. 

381. Net energy in maintenance rations. — A considerable 
number of earlier experiments are also on record in which the 
amounts of net energy contained in actual maintenance rations 
of cattle may be computed with more or less accuracy. 

The early experiments of Henneberg and Stohmann, on which 
was based Wolff's feeding standard for maintenance long cur- 
rent, as well as a considerable number of subsequent ones, 3 
have now chiefly an historic interest. Of the later investiga- 
tions, by far the most important are those by G. Kiihn and by 
Kellner 4 in which approximate maintenance rations were fed; 
The small gains or losses of protein and fat by the animals were 
determined by means of a Pettenkofer respiration apparatus 
and corrected for upon the basis of results obtained in other 
respiration experiments on productive rations, and in this way 
the metabolizable energy required for maintenance was com- 
puted. 

1 Eight of them have been reported. U. S. Dept. Agr., Bur. Anim. Indus,, 
Buls. 74, ioi, and 128. 

2 In the manner described in Jour. Agr. Research, 3 (191 5), 454. 

3 Compare Penna. Expt. Sta., Bui. 42 (1898), pp. 8-21. 

4 Reported by Kellner: Landw. Vers. Sta., 53 (1900), pp. 6-16, 



MAINTENANCE — THE ENERGY REQUIREMENTS 291 



In addition to these respiration experiments, investigations 
upon the live weight maintenance of cattle made by the writer, 1 
by Haecker, 2 and by Evvard 3 have been discussed elsewhere 4 
by the writer. 

Table 48. — Net Energy in Daily Maintenance Rations of Cattle 











Per iooo Pounds 


3 to 

0% 








Live Weight 


fig 










in a 




Feed 


of Animals 


£ 


E 




w 








M £ 


2 2 
E £ 




6 x 








a J 


3 1* 






Respiration 














experiments 












17 


Armsby and Fries . 


Roughage 5 


Medium 


7.430 


4.723 


5.936 


5 


Armsby and Fries . 


Mixed rations 5 


Medium 


6.474 


5.90O 


6.194 


22 


Armsby and Fries . 


Average of all 5 


Medium 


7.430 


4.723 


5-995 


7 


Kellner .... 


Roughage 


Medium 


6.780 


4.921 


5-742 


29 


Average 6 . . . 










5-934 




Kellner .... 


Mixed rations 


Fat 


8.871 


7.319 


7.946 




Live weight 














experiments 












10 


Armsby .... 


(Hay only) 


Thin 


7.044 


6.136 


6.505 


3 


Armsby .... 


(Mixed rations) 


Thin 


6.039 


4.7I3 


5-423 


6 


Haecker .... 




Medium 


5.676 


4.662 


5.021 


3 


Evvard, 1st 60-day 














expt 


Mixed rations 


Medium 


7.850 


6.450 


7.180 


1 


Evvard, 362-day 
















Mixed rations 


Medium 


— 


— 


8.090 


7 


Eckles .... 
Average 6 . . . 


Mixed rations 


Medium 


7.079 


5.841 


6.173 
6.181 


3 


Eward, 2d 60-day 


Mixed rations 


Partly 










experiment 




fattened 


10.620 


8.150 


9.070 



For the purpose of computing the approximate net energy 
values of these rations it seems permissible to assume provi- 
sionally that the same proportion of their metabolizable energy 



1 Penna. Expt. Sta., Bui. 42 (1898). 2 Minn. Expt. Sta., Bui. 79. 

3 Thesis for degree of M. S., University of Missouri, 1909. 
4 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 143, 44-46. 

5 Omitting the experiment on alfalfa meal. 

6 Giving each experiment equal weight. 



292 NUTRITION OF FARM ANIMALS 

was available for maintenance as in the case of the hays exclu- 
sive of alfalfa investigated by Armsby and Fries, 1 viz., 52.8 per 
cent. For the mixed rations a percentage of 55 has been as- 
sumed. In Evvard's experiments the net energy was computed 
by that investigator. Eckles 2 has also reported five determi- 
nations of the live weight maintenance of dry cows in which 
the net energy values of the mixed rations consumed were 
estimated from the writer's computed averages. 3 

The results of the computations are shown in Table 48, 
Armsby and Fries' determinations of the net energy require- 
ment being included for comparison. 

For the medium and thin animals, the estimated net energy 
of Kellner's maintenance rations is distinctly less than the 
average maintenance requirement found in Armsby and Fries' 
experiments. The mean of the individual results of the two 
experimenters, on 16 different animals, is 5934 Cals. The 
average estimated net energy in the maintenance rations of the 
live weight experiments is somewhat greater, viz., 6 181 Cals., 
although if the one apparently exceptional result obtained by 
Evvard be omitted, the average is reduced to 61 13 Cals. The 
maintenance requirement of fat cattle is evidently distinctly 
greater than that in the unfattened state but the data are too 
few to permit the statement of a trustworthy average. 

It appears, then, that the maintenance ration of mature 
cattle in thin to medium condition must supply, on the aver- 
age, about 6000 Cals. of net energy per thousand pounds live 
weight, although with considerable variations from this average 
in individual cases. That the actual weight of feeding stuffs 
required to constitute a maintenance ration, as well as the 
quantities of metabolizable energy contained in it, will vary 
with the kinds of feeds used has already been pointed out 
(375) and is indeed sufficiently obvious. 

The maintenance requirement of sheep 

382. Metabolizable energy in maintenance rations. — Data 
regarding the maintenance ration of sheep are much less abun- 
dant than those for cattle and no experiments have been re- 

1 Jour. Agr. Research, 3 (1915), 484-485. 

2 Mo. Expt. Sta., Research Bui. 7, p. 120. 
3 U. S. Dept. Agr., Farmers' Bui. 346, p. 15. 



MAINTENANCE — THE ENERGY REQUIREMENTS 293 

ported in which the net energy required for maintenance, i.e., 
the fasting katabolism, has been determined. 

Respiration experiments upon sheep have been made by 
Henneberg and Stohmann l in 1867-1868 on two animals, by 
Henneberg, Fleisher and Miiller 2 in 1872 upon two animals, 
by Hagemann 3 in 1899 on one animal, and by Kellner 4 upon 
one animal. With the exception of the third, these were bal- 
ance experiments with a Pettenkofer apparatus and included 
no direct determinations of energy so far as reported. The 
third investigation comprised a digestion and metabolism 
experiment in which the energy of the feed and the visible ex- 
creta was determined directly and also 42 determinations 
of the pulmonary respiration with the Zuntz type of apparatus. 
(299). 

In addition to the foregoing respiration experiments there are 
a number of digestion experiments by Wolff in which the 
live weight of the animals was approximately maintained, 5 and 
Henry 6 reports a series of experiments by Carlyle and Klein- 
heinz with breeding ewes in which various mixed rations pro- 
duced an average daily gain of 0.16 pound per head in animals 
averaging 145 pounds in weight. 

In these experiments the metabolizable energy of the rations 
may be computed approximately from the digestible organic 
matter in the manner described in Chapter XVII (774). In 
the respiration experiments a correction for the gain or loss by 
the animal may be made as in the case of Kellner' s experiments 
on cattle (381), while an approximate correction for the gain in 
the live weight experiments may also be made. 

The results, computed per 100 lb. live weight, are shown in 
Table 49. 

383. Net energy in maintenance rations of sheep. — As al- 
ready stated, no direct determinations of the net energy re- 
quired for the maintenance of sheep are on record and only 
unsatisfactory data are available for computing it from the 
metabolizable energy of maintenance rations. For the fore- 

1 Neue Beitrage, etc., pp. 68-286. 

2 Jahresber. Agr. Chem., 16-17 (1873-74), H, 145. 

3 Arch. (Anat. u.) Physiol. ; 1899, Suppl., p. 138. 

4 Die Ernahrung. landw. Nutzt., 6th Ed., p. 422. 

5 Compare U. S. Dept. of Agr., Bur. Anim. Indus., Bui. 143 (191 2), pp. 49~5i- 

6 Feeds and Feeding, 10th Ed., p. 482. 



294 



NUTRITION OF FARM ANIMALS 



going experiments, however, it may be permissible to assume, 
as in the case of cattle, that about 52.8 per cent of the metab- 
olizable energy of roughage and 55 per cent of that of mixed 
rations was available for maintenance. The results of a com- 
putation upon this basis are contained in the last column of the 
following table. They possess a certain degree of interest, 
although obviously they are of uncertain value. 

Table 49. — Energy in Daily Maintenance Rations of Sheep 



Respiration experiments 

Ffenneberg and Stohmann . . . 
Henneberg, Fleischer and Muller 

Kellner 

Hagemann 

Average 

Live weight experiments 

Wolff, 1871, 6 experiments . . 
Wolff, 1892-1893, 8 experiments 
Carlyle and Klienheinz . . . . 

Average 

Average of all 



Per 100 Lb. Live Weight 



Metaboliz- 

able 

Energy 



Therms 

1-475 
I.420 
I. no 
1.282 



1.322 



1.634 
1.72s 
1.513 



1.624 

1.368 



Net 
Energy 



Therms 

•779 
.781 
.611 

.705 



.719 



.863 
.863 
.832 



.853 
.791 



384. Comparison of sheep with cattle. — It is of some interest 
to compare the maintenance requirement of sheep with that of 
cattle. Since the sheep is a much smaller animal than the steer 
it naturally requires relatively more feed in proportion to its 
weight (345), as the foregoing figures show to be the case. 
As compared with a steer weighing 1000 pounds, ten sheep weigh- 
ing 100 pounds each would require for maintenance, according 
to the foregoing estimates, about 30 per cent more energy. 
If, however, the comparison be made in proportion to the two- 
thirds power of the live weight, i.e., substantially in propor- 
tion to the body surface (347), a very different result is reached, 
the maintenance ration of the sheep as thus computed amount- 
ing to little more than 60 per cent of that of cattle. 



MAINTENANCE — THE ENERGY REQUIREMENTS 295 

Table 50. — Maintenance Requirements of Cattle and Sheep. 
Computed in Proportion to Body Surface 





Net Energy 
Therms 




6.000 
3.670 



While such a comparison is of course but a rough approxi- 
mation, it nevertheless seems to show conclusively that the 
metabolism of the sheep per unit of surface is distinctly lower 
than that of cattle, so that this animal apparently constitutes 
an exception to the results computed by E. Voit (345) for 
several other species. The thick coat of wool, of course, tends 
to reduce the rate at which heat is lost from the body and it 
seems at least a plausible conjecture that in the course of or- 
ganic evolution the intensity of metabolism and the rate of heat 
radiation may have undergone mutual adjustment. 

The maintenance requirement of the horse 

385. Net energy requirement. — Zuntz and Hagemann l 
have computed the fasting katabolism of the horse from the 
results of numerous short respiration experiments with the 
Zuntz type of apparatus (299) by means of a comparison identi- 
cal in principle with that already described for cattle (374) 
but carried out by quite a different method, involving numerous 
estimates and computations. 

They assume, on the basis of experiments on man, that 9 per 
cent of the metabolizable energy of the digestible nutrients consumed 
by a horse is converted into heat in the process of digestion, and com- 
pute from their own experiments that each gram of total crude fiber 
consumed increases the heat production by 2.086 Cals. additional, 
exclusive of that due to mastication. For the purpose of computing 
the fasting energy expenditure, those rest experiments on Horse III 
in which the feed consisted of oats, hay and straw, are used. On 
the basis of a number of short respiration experiments made within 
the first five hours after feeding, the total energy metabolism per day 

J Landw. Jahrb., 27 (1898), Ergzbd, III, 271-285 and 422-425. 



296 



NUTRITION OF FARM ANIMALS 



on the various rations is computed from the results of five previous 
balance experiments on similar rations by combining them in various 
ratios according to the proportions of oats, hay and straw consumed. 
From this is subtracted the heat computed to have been produced in 
the digestion of the feed (not including the work of mastication), 
the remainder showing, of course, the katabolism due to internal 
work, i.e., the net energy requirement. 1 

Table 51 shows for the eight experiments compared the 
total estimated heat production per day, the computed energy 
expenditure caused by the consumption of the feed, and by dif- 
ference the energy expenditure in the fasting state, i.e., the net 
energy requirement for maintenance. 

Table 51. — Net Energy Requirement for Maintenance of Horse 







< 
W 


Feed 





Energy 

Expenditure 
in Fasting 




Periods 


« 
O 

H 

w 

w 
> 

(J 


^ S5 
Q O 
W H 

h q 


en 
O 


a 

CO 


>> 

w 


Computed Ei 
Expenditure 
Due to Feed 


T3 

4) 

X 

t-l 

Ph 


Per Square 
Centimeter 
Body Surface 


Season 




Kgs. 


Cals. 


Kgs. 


Kgs. 


Kgs. 


Cals. 


Cals. 


Cals. 




a 


428.1 


12,541 


6 


1 


7 


8403 


4138 


80.7 


Winter 


b 


434-1 


11,674 


6 


1 


6 


7704 


397o 


76.7 


Summer 


e 


45°-4 


12,364 


6 


1 


6 


7704 


4660 


87.9 


Winter 


f 


449.1 


11,783 


6 


1 


4-75 


6830 


4953 


93-6 


Summer 


1 


440.1 


11,893 


6 


1 


6 


7704 


4189 


80.2 


Winter 


n 


448.2 


11,407 


4-8 





5-i 


5672 


5735 


108.5 


Summer 


c 


442.2 


12,450 








10.5 


7340 


5110 


97.6 


Summer 


No. 1 1 8c 


434-6 


11,021 


4.8 


0.8 


1.88 


4122 


6899 


133-3 


Winter 



In the experiments with a standard ration of 6 kgs. of oats, 
one of straw, and six (or seven) of hay, the average computed 
fasting katabolism per day in three winter periods was 4.33 
Therms, while in a single summer period it reaches the minimum 
of 3.97 Therms per head, or 4.08 Therms per 1000 pounds live 
weight. Zuntz and Hagemann consider that the latter amount 
represents approximately the minimum requirement for the in- 



1 For a more complete account of the method, compare the writer's Principles 
of Animal Nutrition, pp. 386-387. 



MAINTENANCE — THE ENERGY REQUIREMENTS 297 

ternal work and regard the higher figures obtained in the winter 
experiments a3 indicating a stimulation of the heat production 
by the low temperature to which the animal was exposed ; i.e., 
they consider that the experiments were made below the critical 
temperature. The notably higher results obtained with lighter 
rations they ascribe to a similar cause, viz., that the heat arising 
from the work of digestion, together with that due to the neces- 
sary internal work (fasting katabolism), was insufficient to 
maintain the body temperature. 

It must be confessed that, in view of the more active, tem- 
perament of the horse as compared with cattle this relatively 
low figure for the fasting katabolism is rather surprising, and 
the fact should not be overlooked that it is derived from short 
periods in which it is probable that the animal was unusually 
quiet. It perhaps represents more nearly the physiological 
than the economic minimum of net energy required for main- 
tenance, and it would be of much interest to compare it with 
the results of 24-hour experiments. 

386. Metabolizable energy in maintenance rations. — A 
considerable number of experiments are on record in which 
the amount of total digestible matter required for the main- 
tenance of the horse has been determined. 

The maintenance rations of cattle and sheep may be deter- 
mined with a good degree of accuracy by varying the quantity 
of feed given until equality between income and outgo or con- 
stancy of live weight is attained, but this method is not fully 
applicable to the horse. Owing to his more active tempera- 
ment, feed seems to exert a greater stimulus upon his muscular 
activity than is the case with the more phlegmatic ruminants, 
so that a considerable excess over an actual maintenance 
ration may be consumed by a horse and expended in the 
various minor activities noted in Chapter VII (348), while 
the balance of income and outgo may show neither gain 
nor loss, i.e., may appear to show that the ration is a main- 
tenance ration. 

a. Wolffs determinations. — One method of avoiding this 
difficulty and determining the true maintenance ration is that 
employed by Wolff in his extensive investigations * upon work 
production by the horse (670, 779). In these experiments the 

1 Compare the writer's Principles of Animal Nutrition, pp. 53i _ 535- 



298 NUTRITION OF FARM ANIMALS 

horse performed a measured amount of work } which was so 
adjusted in different periods as to be as nearly as possible in 
equilibrium with the feed consumed. This was considered to 
be the case when the live weight of the animal remained sub- 
stantially unchanged for a considerable period and when the 
urinary nitrogen did not show an increase as a consequence 
of the additional work done (637). By comparing the work 
performed on a basal ration with that which could be done with 
a heavier one, the ratio of the work done to the additional 
feed consumed was established within the limits of error of the 
method, this being the prime object of the experiments. This 
being determined, however, it was a simple matter to com- 
pute the amount of feed corresponding to the total work per- 
formed, while the difference between the latter and the total 
ration evidently was the maintenance ration. From the total 
digestible nutrients (inclusive of crude fiber) required for main- 
tenance, as thus computed by Wolff, the equivalent amounts of 
metabolizable energy required for maintenance may also be 
computed approximately by the use of Zuntz and Hagemann's 
factor of 3.96 Cals. per gram (776). 

In Wolff's earlier experiments and in those later ones in 
which approximately equal proportions of hay and grain were 
consumed, the maintenance ration was found to be approxi- 
mately 4200 grams total nutrients per 500 kgs. live weight, 
equivalent to 16.63 Therms. In those later experiments (in- 
cluding the results of similar investigations by Grandeau as re- 
computed by Wolff) in which a larger proportion of grain was 
fed, the total nutrients required for maintenance ranged from 
3600 to 3800 grams, equivalent to from 14.26 to 15.05 Therms. 
In other words, the amount of metabolizable energy required 
for maintenance varied with the proportion of roughage pres- 
ent, as would be anticipated from the results with cattle re- 
corded on previous pages. 

b. Zuntz and Hagemann's results. — From a respiration ex- 
periment at the Gottingen Experiment Station, Zuntz and Hage- 
mann compute the metabolizable energy of the maintenance 

1 Wolff's experiments were made with a sweep-power arranged to serve also as a 
dynamometer. The actual measurements of the work performed, except in the later 
experiments, proved to be too low, but Wolff believes them to be relatively correct, 
so that the ratio between the work as measured and the additional feed required to 
produce it may still serve as the basis of computation. 



MAINTENANCE — THE ENERGY REQUIREMENTS 299 

ration of the horse by subtracting from the total digested 
nutrients the carbohydrate equivalent of the protein and fat 
.gained by the animal, disregarding the possible stimulating 
effect of the feed. In this way, they find for the maintenance 
ration 2955.4 grams total digested nutrients per head, equiva- 
lent to 11.70 Therms or 1 2.1 Therms per 1000 pounds live weight, 
a result notablv lower than Wolff's. This difference is ascribed 
by Zuntz and Hagemann to the larger content of crude fiber in 
Wolff's rations, the work of digestion of this ingredient as es- 
timated by them (777) very nearly accounting for the differ- 

ence. 

c. Muntz's experiments.— Miintz * in 1878-1879 attempted to 
determine the maintenance ration of the horse by starting with 
an insufficient ration and gradually increasing it until an equilib- 
rium between feed and live weight was secured, seeking in this 
manner to eliminate the stimulating effect of excess feed (392). 
The trials were made on the horses of the Paris Omnibus Com- 
pany, their work ration being known from previous experiments. 
He found that a ration equal to A of the work ration and 
which may be estimated to contain 12.1 Therms of metabohz- 
able energy per 1000 pounds live weight was slightly more than 
sufficient for maintenance. 

d. Grandeau and LeClerc's results. — Grandeau and LeClerc, 2 
in addition to the experiments mentioned in connection with 
Wolff's results, fed five cab horses a ration of 8 kgs. of hay 
during a total of 14 periods of a month each (one to five periods 
for each animal) during each of which the digestibility of the 
ration was determined. On the average of all the periods, the 
results per day and head were as follows : — 

Total digestible nutrients (fat X 2.4) . • • • 2 7 8 3-7 grams 
Equivalent metabolizable energy at 3.96 Cals. per 

gram 11.03 Therms 

Daily gain in weight °-*9 kg. 

Average live weight 393 - 6 kgs. 

The foregoing ration, which was evidently somewhat more 
than a maintenance ration, is equivalent to 13. 1 Therms of 
metabolizable energy per 1000 pounds live weight. This is 

1 Annales de l'Institut National Agronomique, Tome 3, 1876-1879. 

2 L'alimentation du Cheval de Trait, 1883, III. 



3°° 



NUTRITION OF FARM ANIMALS 



materially less than was obtained in Wolff's earlier experiments 
with hay and about the same as that found by him and by 
Zuntz and Hagemann for rations containing much grain. 

The following summary of the data regarding the metaboliz- 
able energy required for maintenance by the horse shows a 
considerable range of variation which is only partially expli- 
cable by the varying proportions of grain and roughage con- 
tained in the rations. 

Table 52. — Maintenance Rations of the Horse 



Experimenter 



Wolff 

Wolff and Grandeau and LeClerc 
Zuntz and Hagemann . . . . 

Muntz 

Grandeau and LeClerc . . . . 
Wolff 



Grain to One 
of Roughage 


Metabolizable 

Energy per 

1000 lb. Live 

Weight 


(Approximate) 


Therms 


1.0 


15-6 


2.4 


13.6 


1.8 


12. 1 


0.7 
hay only 
hay only 


12. 1 

17.1 



387. Metabolizable compared with net energy requirement. 

— The net energy required for maintenance, as with other ani- 
mals, equals of course the fasting katabolism. This Zuntz and 
Hagemann compute, in the manner already described (385) to 
be 4.1 Therms per thousand pounds live weight. As was 
there pointed out, however, those of their experiments in which 
the external temperature was lower or the amount of feed less 
gave higher results. The latter was also notably the case in 
earlier experiments in which still lighter rations were fed. 

On the average of the eight most satisfactory experiments out of 
twelve l on Horse II the total katabolism per day and head was 1 1.027 
Therms upon a ration consisting of 3.5 Kgs. of oats, 0.5 of straw and 
2.5 of hay. Computed in the same manner as in Table 51, the 
expenditure of energy in the digestion of this ration is equal to 
3782 Cals., which leaves a remainder of 7244 Cals., equivalent to 
140.3 Cals., per square centimeter of surface. This is a higher 
figure than any of those contained in Table 51, although the total 
katabolism was not notably different. 

1 Landw. Jahrb., 18, 1 ; 27, Ergzbd. Ill, 356-357. 



MAINTENANCE — THE ENERGY REQUIREMENTS 301 

The authors conclude, therefore, that when the amount of 
heat liberated by the digestive work is small the lack is com- 
pensated for by an increased katabolism of body tissue. Their 
final result is that their animal required per head at least 11.00 
Therms of heat to maintain his body temperature. In other 
words, this is the minimum of metabolizable energy which 
must be contained in a maintenance ration, since if less be 
present, even although the ration supply the requisite amount 
of net energy, body tissue would still be katabolized for the 
production of the necessary heat. Computed per thousand 
pounds live weight, Zuntz and Hagemann's estimated main- 
tenance requirement is : — 

Net energy for internal work 4.1 Therms 

Additional required for heat production 7.8 Therms 

Total metabolizable energy required 11.9 Therms 

In computing a ration for the actual maintenance of the 
horse at rest, it is necessary, according to these figures, to con- 
sider not only whether it supplies net energy equal to the fast- 
ing katabolism but also whether it contains sufficient metab- 
olizable energy to support the necessary heat production. On 
the other hand no such allowance need ordinarily be made in 
computing work rations. The horse when at work is producing 
an excess of heat (compare Chapter XIV), and during the work- 
ing hours no expenditure of feed energy for the sake of heat 
production would be called for, while any ordinary working 
ration would probably contain a considerable surplus of me- 
tabolizable energy over the maintenance demand during the 
hours of rest. 

The maintenance requirement of fowls 

388. Net energy requirements. — Gerhartz * has measured 
the net energy requirement of fowls by means of a num- 
ber of respiration experiments with the Regnault-Reiset type 
of apparatus (298) upon two fasting hens. He has also com- 
puted the fasting katabolism from a number of respiration ex- 
periments in which the animals were fed by subtracting from 
the total metabolism that computed to have been due to the 

1 Landw. Jahrb., 46 (1914), 797. 



3° 2 



NUTRITION OF FARM ANIMALS 



consumption of the feed — i.e., by substantially the same gen- 
eral methods used by Zuntz and Hagemann for the horse (385). 
His results, computed per thousand square centimeters of body 
surface and also per 5 pounds live weight in proportion to the 
§ power of the latter, were as follows : — 

Table 53. — Net Energy for Maintenance of Hens 



In fasting experiments 

Minimum when not laying . . 

Average when not laying . . . . 

Average when laying . . . . . . 

Computed from experiments with feed 
Minimum when not laying . . . . 
Average when not laying . . . . 
Average when laying 



Live 

Weight 


Per iooo 

Sq. Cm. 

Body 

Surface 


Grms. 


Cals. 


2350 
2273 

2350 


58.37 
76.77 
93-65 


2137 
2046 


52.98 
62.16 


2023 


87.03 



Per s 
Pounds 

Live 
Weight 



Cals. 

57-oi 
76.75 
91-45 



55-13 

66.58 

93-91 



It would appear from the figures that the average main- 
tenance requirement of a 5-pound hen may be estimated at ap- 
proximately 72 Cals., while in periods of minimum muscular ac- 
tivity it may fall as low as 56 Cals. The much higher figure 
(93 Cals.) obtained in the periods when the hen was laying 
does not represent maintenance simply, but includes also the 
energy expended in the formation of the egg. As with all small 
animals, the katabolism of the hen per unit weight is high, but 
when computed per unit of surface it does not differ greatly 
from that of other species. 

389. Metabolizable energy in maintenance rations. — Ger- 
hartz also determined the amount of feed required to main- 
tain the live weight of his fowls and computes the correspond- 
ing amounts of metabolizable energy to have been per iooo sq. 
cm. body surface. 

Rest period 102 Cals. 

Molting period 107 Cals. 

f ^ 2 Cals 
Brooding period { '„ Cals ! 

Average 95 Cals. 



MAINTENANCE — THE ENERGY REQUIREMENTS 303 

Summary 

390. For convenience of reference, the average results re- 
garding the energy required for the maintenance of the com- 
mon species of farm animals as recorded in the foregoing pages 
are brought together in the following table. For live weights 
other than those stated the maintenance requirement may be 
computed in proportion to the surface in the manner described 
in Chapter VII (347). 

Table 54. — Energy Requirements for Maintenance 



Swine, per 100 lb. live weight . 
Cattle, per 1000 lb. live weight 

Unfattened 

Fattened 

Sheep, per 100 lb. live weight . 
Horses, per 1000 lb. live weight 
Hens, per 5 lb. live weight 




Metabolizable 
Energy 

Therms 



i-53 

10,47 
13-55 

1-37 
11.90 

0.095 



As pointed out at the beginning of this section (376), the 
foregoing figures express an economic rather than a physio- 
logical requirement for energy. Besides the absolute energy 
requirement in a state of complete rest, they include the energy 
expended in divers forms of incidental muscular work, of which 
one of the most important, in farm animals, appears to be that 
of standing (349). The average for swine was obtained from 
experiments in which the animals were lying during most or all 
of the time. The average for cattle, as noted, has been com- 
puted to twelve hours standing, while that for the horse rep- 
resents the katabolism when standing quietly. 

Moreover, even with the limitations just indicated, the results 
represent averages from which the energy expenditure of the 
individual animal may differ considerably. Such averages are 
useful as a basis for computing feed requirements and rations, 
but it should be clearly understood that they are by no means 
physiological constants which can be applied to all animals 



3°4 



NUTRITION OF FARM ANIMALS 



indiscriminately or used as a basis for exact computations of 
the effects of feeds ill individual cases. 

§ 3. Factors Affecting the Maintenance Requirement 

Certain conditions which affect the energy expenditure of 
the fasting animal, and therefore the amount of net energy 
required for maintenance, have already been discussed in Chap- 
ter VII (345-357) , while a few others may be more conveniently 
considered at this point. 

391. Temperament. — The nervous, restless animal is con- 
tinually expending energy in a variety of unnecessary move- 
ments which may very materially increase the amount of energy 
needed for his maintenance as compared with that required 
by the quieter and more phlegmatic animal. There can be little 
question that those differences between the maintenance re- 
quirements of different animals which are ascribed somewhat 
vaguely to " individuality " are due to a large extent to vary- 
ing amounts of muscular activity. 

Thus in Armsby and Fries' determinations * of the maintenance 
requirement of cattle (380) the two animals designated as A 
and B were respectively a pure-bred beef animal and a scrub, the 
latter having more or less dairy blood and being of a decidedly 
more nervous disposition than the animal A. The difference 
in the requirements of the two animals, as shown by the follow- 
ing comparison, may be reasonably ascribed to this differ- 
ence in temperament. 

Table 55. — Net Energy Requirement for Maintenance 



Year 



1905 • • 

1906 . . 

1907 . . 
Average 




Scrub 

Steer 

B 



Therms 

6.052 

6.305 
6.067 

6. 141 



1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128 (1911), p. 53. 



MAINTENANCE — THE ENERGY REQUIREMENTS 305 

Like the temperament, any external conditions tending to 
affect the degree of muscular activity will also tend to affect 
the maintenance requirement. The steer confined in a stall, 
for example, may take less muscular exercise, and therefore 
require less energy for maintenance, than one simply confined 
to a pen or open yard. The animal comfortably bedded and 
thereby induced to spend much of his time lying down will 
consume a smaller proportion of his feed for maintenance than 
one kept under less comfortable conditions. Any sort of 
excitement is likely to be paid for by increased muscular ac- 
tivity and correspondingly increased consumption of feed for 
maintenance. 

392. The plane of nutrition. — It is somewhat generally be- 
lieved that the amount of feed necessary for maintenance varies 
with the plane of nutrition on which the animal is kept. By 
this is meant that an animal which has been highly fed for 
some time will require a larger amount' of feed for maintenance 
than a similar animal which has been sparsely fed and is in 
a more or less reduced condition. Thus, Waters 1 writes : 
" Apparently the animal organism when kept for a long 
period of time on a low nutritive plane, as in the case of main- 
tenance animals, gets on a more economical basis than when 
more liberally fed. For example, if we reduce the feed of an 
animal that has been previously liberally nourished to a point 
where for a month or more there is a small loss in weight, an 
equilibrium will later be established and subsequently the 
animal may increase in weight, the quantity and quality of 
the feed remaining the same. Thus a ration that was insuf- 
ficient to sustain live weight at first may be capable later of 
maintaining the animal at a stationary body weight, and still 
later of causing an increase in weight. Digestion experiments 
with a number of animals indicate that a part of this is due to 
the more complete digestion of the feed by the animal on a low 
nutritive plane, but so far as the experiments have thus far pro- 
gressed there does not seem to have been a sufficient increase 
in the degree to which the feed has been digested to account 
for all the increased efficiency in the ration noted." 2 

Comparatively little experimental confirmation of these re- 
sults has as yet been published, although respiration experi- 

1 Proc. Soc. Prom. Agr. Sci., 1908, p. 96. - Compare Chapter XVI, § 3 (722). 
X 



306 NUTRITION OF FARM ANIMALS 

ments on dogs by Kleinert 1 and by Schlossmann and Mursch- 
hauser 2 seem to point in the same direction. 

Observations made by Zuntz and Hagemann 3 on the horse 
appear suggestive in this connection. In a series of respiration 
experiments they have confirmed the common observation that 
a surplus of feed above the maintenance requirement stimu- 
lates the muscular activity and restlessness of this animal, so 
that a ration may be considerably more than sufficient to main- 
tain the animal when standing quietly in the stall and yet 
give rise to no increase in weight under ordinary conditions. 
A similar stimulating effect of the feed upon the minor muscular 
movements of cattle, expecially while standing, seems to be in- 
dicated by the experiments of Armsby and Fries (367 e). It 
seems possible that part, at least, of the diminution of the main- 
tenance requirement observed by Waters may have been due 
to a voluntary restriction of motion on the part of the animals 
on the low nutritive plane. 

In attempting to determine experimentally the minimum 
maintenance requirement it is evidently the safer method of 
procedure, especially with the horse, to approach the main- 
tenance point by gradually increasing a sub-maintenance ration, 
as in Miintz's experiments on the horse (386 c) and those of 
Armsby and Fries on cattle (374) rather than by the gradual 
reduction of a supermaintenance ration. 

393. Fattening. — That fat animals have a relatively greater 
maintenance requirement than thin ones seems to be fairly 
well established for cattle by the experiments of Kellner and 
of Evvard, the results of which are recorded in Table 48 (381). 

One obvious reason why the maintenance requirement per 
head should be greater for a fattened animal than for the same 
animal before fattening is the greater muscular effort expended 
in standing, due to the greater weight to be supported. Zuntz 
and Hagemann, in experiments upon the horse carrying weight 
on its back, found that this increase was proportional to the 
amount of weight added (665). If this be true generally, then 
that portion of the metabolism due to standing will increase 
more rapidly than the body surface. In Armsby and Fries' 
experiments on unfatted cattle, however, the energy expendi- 

1 Ztschr. Biol., 61 (1913), 346. s Biochem. Ztschr., 53 (1013), 265. 

3 Landw. Jahrb. 27 (1898), Ergzbd. Ill, 211, 236. 



MAINTENANCE — THE ENERGY REQUIREMENTS 307 

ture due to standing 12 hours amounted to only about 15 per 
cent of the total daily metabolism. The increase in the main- 
tenance requirement per unit of surface which is indicated by 
Kellner's results is considerably greater than would be computed 
on this basis and the same is true of Evvard's fat animals, the 
difference becoming greater as the animals grew fatter. 

394. Age. — The maintenance requirement of a young ani- 
mal is naturally smaller per head than that of an older animal 
on account of the difference in size. Whether there is any 
difference in the relative requirement, that is, in the require- 
ment computed to uniform weight or surface, is not altogether 
clear, few specific results on farm animals being on record. 
Evvard's results on yearlings (381) are somewhat higher than 
most of those which have been obtained with mature cat- 
tle, although, of course, these figures do not relate to the same 
individuals at different ages. Armsby and Fries x in a series of 
respiration calorimeter experiments upon the same two animals 
in three successive years found with their full-blood steer a 
marked decrease in the maintenance requirement as a yearling 
and as a three-year old, when corrected to a uniform number of 
hours standing and computed in proportion to the two-thirds 
power of the weight. With the scrub steer, on the other 
hand, no distinct decrease of the maintenance requirement was 
observed. 

Somewhat extensive data are on record regarding the metabolism 
of man at different ages. A summary of these by Tigerstedt 2 seems 
to show clearly that the metabolism per unit of surface diminishes, 
although, not very rapidly, from youth to maturity. In view of the 
relatively slow growth of man, these results are comparable to such 
as might be obtained during the first six to twelve months of the life 
of ordinary domestic animals and for these ages there are no satis- 
factory determinations of the maintenance requirement. 

If it be true that the maintenance requirement of a young 
animal is relatively greater than that of an older one, this may 
fairly be presumed to be due to a considerable extent to the 
greater muscular activity usually exhibited by young animals, 
which, as already pointed out, notably increases the body 
katabolism. 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128. 

2 Nagel's Handbuch der Physiologie des Menschen, I, 469. 



308 NUTRITION OF FARM ANIMALS 

§ 4. The Relation of the Maintenance Requirement 
to External Temperature 

While the temperature to which an animal is exposed is but 
one among other factors which may affect its maintenance re- 
quirement, the somewhat complicated relations involved seem 
to warrant a separate discussion. 

395. Feed consumption lowers the critical temperature. — In 
discussing the influence of temperature upon the fasting katab- 
olism (350-357) it was shown that for the fasting animal there 
is a certain external temperature (or more strictly, thermal en- 
vironment), called the " critical temperature," at which the 
heat production incidental to the necessary fasting katabolism 
just balances the unavoidable loss by radiation, conduction and 
evaporation, so that the body temperature is just maintained. 
Above this temperature, the fasting animal has a surplus of 
heat which it gets rid of by means of the physical regulation. 
Below the critical temperature, on the other hand, its katab- 
olism is increased beyond that necessary for the internal work 
of the body in order to supply the necessary amount of heat; 
i.e., the energy expenditure is augmented. 

As has been shown (365), however, the consumption of feed 
results in increasing the heat production of an animal. When 
an animal is fed, therefore, it has two sources of heat : first, as 
in the fasting state, the heat resulting from the katabolism inci- 
dent to the necessary internal work of the body, and second, in 
addition to this, the heat generated by the so-called " work of 
digestion." Under these conditions, with more heat being 
produced in the body as the result of feed consumption, it is 
obvious that the animal can withstand a greater cooling effect 
of its surroundings without being compelled to katabolize body 
substance to maintain its body temperature. In other words, 
the " critical temperature " is lowered. Furthermore, the 
greater the amount of feed consumed the lower is the point to 
which the external temperature can fall without reaching the 
critical point, so that animals receiving heavy rations in pro- 
ductive feeding can withstand more cold than those on simple 
maintenance. Conversely, for any particular temperature 
there will be a definite amount of any given feed the consumption 
of which, together with the katabolism required for the internal 



MAINTENANCE — THE ENERGY REQUIREMENTS 309 

work, will give rise to the production of an amount of heat 
just sufficient to balance the unavoidable loss of heat to the 
surroundings. 

This influence of the quantity of feed is well illustrated by 
the following tabulation of Rubner's results upon a dog at 
different temperatures and consuming different amounts of 
meat. 

Table 56. — Influence of External Temperature on Heat 

Production 





Heat Production per Kg. Body Weight 


Temperature 












Fasting 


Fed 100 Grms. 


Fed 200 Grms. 


Fed 320 Grms. 




Meat 


Meat 


Meat 




Cals. 


Cals. 


Cals. 


Cals. 


7°C. 


86.4 


— 


77-7 


87.9 


15° C. 


63.O 


— 


— 


86.6 


20°C. 


55-9 


55-9 


57-9 


76.3 


25° C. 


54-2 


55-5 


64.9 


— 


30°C. 


56.2 


55-6 


63-4 


83.0 



The amount of feed required to just offset the cooling effect 
of a low temperature might be called the critical amount of 
feed for that temperature. It will obviously be less the greater 
the proportion of its metabolizable energy which is dissipated 
as heat. 

For example, in discussing the relative amounts of different 
feeds necessary for maintenance (375) it was stated that either 
13.83 lb. of mixed hay or 9.07 lb. of mixed grain and alfalfa 
hay would yield approximately 6.0 Therms of net energy, and 
would therefore constitute a maintenance ration for a 1000- 
pound steer. The amounts of metabolizable energy contained 
in these two rations, however, would be different, viz. : — 



13.83 lb. mixed hay 

9.07 lb. mixed grain and alfalfa hay 



12.01 Therms 
10.69 Therms 



Since both are maintenance rations, the animal would neither 
gain nor lose energy and all the metabolizable energy of the 
feed would be finally converted into heat in both cases. The 



310 NUTRITION OF FARM ANIMALS 

animal on the exclusive hay ration, therefore, would have at 
his disposal 1.32 Therms more heat than the other and accord- 
ingly could withstand a lower temperature without drawing on 
his body for fuel. 

396. Net energy below critical temperature. — Down to the 
critical temperature which corresponds to the particular amount 
and kind of feed consumed, in accordance with the facts brought 
out in the previous paragraphs, only part of the metaboliz- 
able energy serves to maintain the animal. The remainder is 
virtually expended in the " work of digestion " and converted 
into heat, and this heat, since not needed by the animal, be- 
comes an excretum and is gotten rid of. If, however, the ex- 
ternal temperature falls below the critical point the case is dif-. 
ferent. Heat resulting from the ingestion of feed is just as useful 
as heat from any other source for keeping the body warm. 
Under these conditions, therefore, all the metabolizable energy 
of the feed may be of use. Part of it (the net energy) is used 
directly for supporting the necessary internal work of the body, 
while the remainder prevents the necessity of katabolizing tis- 
sue for the sake of heat production and is therefore indirectly 
of use. In other words, the heat resulting from the consumption 
of feed may be substituted for heat which would otherwise 
have to be obtained by the katabolism of tissue. When the 
external temperature falls so low that all the heat produced by 
the digestive work is required for this purpose, obviously all 
the metabolizable energy of the ration is of use directly or in- 
directly to prevent loss of energy from the body and therefore 
all of it appears to be net energy. 

Thus, if the ration of mixed grain and alfalfa hay used as an illus- 
tration in the previous paragraph be fed to a steer whose surround- 
ings are kept at the critical temperature for the fasting animal, the 
6.0 Therms of net energy which the ration supplies will be used to 
support the internal work of the body, and the heat thus produced 
will be just sufficient to maintain the body temperature, while the 
remaining 4.69 Therms of metabolizable energy will be expended in 
superfluous heat production. Suppose, now, that the external tem- 
perature falls to a point at which the fasting katabolism would be 
10.69 Therms instead of 6.0 Therms, i.e., at which this amount of 
heat is necessary to maintain the normal body temperature. The 
necessary internal work of the body still yields 6.0 Therms, as before, 



MAINTENANCE — THE ENERGY REQUIREMENTS 31 1 

while the additional 4.69 Therms of heat resulting from the "work of 
digestion" will be of use in keeping the animal warm and will obviate 
the necessity of its katabolizing body substance for that purpose. 
All the metabolizable energy of the ration, therefore, contributes to 
the maintenance of the animal under these conditions, part directly 
and part indirectly, and the availability is apparently 100 per cent, 
while the real availability for the physiological processes in the body 
is only 56 per cent. If the experiment were made at an intermediate 
temperature at which the fasting metabolism would be 8.0 Therms, 
then 2.0 Therms of the heat due to the "work of digestion" would be 
of use in maintaining the body temperature and the apparent avail- 
ability would be 75 per cent, i.e., the result would be a mixed one. 
Evidently, the actual expenditure of energy in the "work of digestion," 
and its complement, the net energy, can be determined only by ex- 
periments made above the critical temperature. 

397. Bearing on maintenance ration. — The foregoing facts 
render it apparent that in the case of an animal on a main- 
tenance ration the external temperature may fall considerably 
below the critical temperature for the same animal when fast- 
ing before there is any increase in the amount of feed actually 
required for maintenance. Only when the temperature falls so 
low that all the metabolizable energy of the ration is being 
utilized, directly or indirectly, to maintain the body heat will a 
further drop in the temperature call for greater feed consumption, 
i.e., for an increase in the maintenance ration. These considera- 
tions may affect the computation of actual maintenance rations. 
An example of this is afforded by Zuntz and Hagemann's 
results upon the maintenance requirements of the horse (387). 
According to these investigators, a horse weighing 1000 pounds 
requires only 4. 1 Therms of net energy per day for maintenance, 
but the body also needs to be supplied with an additional 7.8 
Therms of heat, making a total of 11.9 Therms daily, to bal- 
ance the loss of heat from the body. If, therefore, a mainte- 
nance ration be computed supplying the necessary 4.1 Therms of 
available energy, it still remains to be considered whether the 
heat arising from the so-called " work of digestion " will supply 
the remaining 7.8 Therms of heat required. If it does not, the 
difference, according to Zuntz and Hagemann, will be made up 
by the katabolism of body tissue, as is illustrated in several of 
their experiments, and the ration will not maintain the animal 
although it contains net energy equal to the fasting katabolism. 



312 NUTRITION OF FARM ANIMALS 

To put the matter in another way, Zuntz and Hagemann con- 
sider that when receiving the ordinary maintenance ration the 
critical external temperature for the horse is comparatively high, 
so that, for example, a ration which is sufficient for maintenance 
in summer may be insufficient in winter, not because it contains 
any less available energy but because it fails to meet the de- 
mand for heat. 

Tangl's experiments (377) showed that the critical tempera- 
ture for swine is likewise comparatively high (68°-73°F.), 
while the expenditure of energy in digestion by these animals, 
especially when fed chiefly or wholly on concentrates, is likely 
to be less than that of ruminants. Exposure to low tempera- 
tures, therefore, may be expected to increase the actual main- 
tenance ration of swine, and this belief seems to be confirmed by 
the reported results upon the influence of exposure on the gains 
of fattening swine. 1 It also seems possible that part of the very 
wide variations observed in the amount of metabolizable energy 
required for the maintenance of swine (378) may be due to dif- 
ferences in the temperature at which the experiments were made. 

Experiments on cattle by Armsby and Fries have shown that 
at temperatures in the neighborhood of 63 ° F., the feed may be 
reduced very considerably below the maintenance ration with- 
out any indication of an increased katabolism for the sake of 
heat production. A single series of comparisons at a somewhat 
lower temperature (56 F.) also showed no increase in the katab- 
olism, even on rations much below maintenance. No exact 
experiments at lower temperatures have been reported. Appar- 
ently, the critical temperature of ruminants is rather low, 
while the " work of digestion " is the source of a relatively 
large amount of heat, so that, under ordinary conditions of feed- 
ing, these animals are producing a surplus of heat and therefore 
a ration supplying net energy sufficient for maintenance is also 
ample as a source of heat. 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), pp. 84-86. 



CHAPTER IX 

MAINTENANCE {Continued) — THE REQUIREMENTS OF 

MATTER 

As was pointed out in the introduction to the previous Chap- 
ter (361), the maintenance requirement is a twofold one, calling 
for the presence in the feed of adequate amounts of certain 
specific substances as well as for an adequate supply of energy. 
The former phase of maintenance in some of its broader aspects 
forms the subject of the present Chapter. These specific sub- 
stances may be grouped for the purpose of this discussion as 
proteins or their constituents, ash ingredients and accessory 
constituents. 



§ i. The Protein Requirements for Maintenance 

398. Nature of protein requirement. — As was shown in 
Chapter VII (340), the loss of protein which the fasting body 
suffers may be interpreted in two ways. First, it may be re- 
garded as due to the complete breaking down of a certain amount 
of protein as the necessary accompaniment of cell activity 
(Rubner's " wear and tear " quota). Second, it may be sup- 
posed that certain atomic groupings contained in the protein 
molecule may be indispensable for the normal functioning of 
the body, so that, if they are not contained in the feed, body 
protein may be katabolized for the sake of obtaining them. 

In either case, it is clear that what the feed must supply in 
order to maintain the body in nitrogen equilibrium is not, 
strictly speaking, protein as such, but materials whose digestive 
cleavage will yield certain amounts and proportions of the con- 
stituent amino acids. On the first hypothesis, the requirements 
for the different " building stones " would be determined sub- 
stantially by the quantities of each existing in the body tissues 

313 



314 NUTRITION OF FARM ANIMALS 

katabolized. According to the second hypothesis, it might 
be presumed that only certain of the atomic groups contained 
in protein, such as tryptophan, e.g., would need to be supplied. 
Moreover, it appears not unlikely that both hypotheses may 
be true and that body protein is katabolized both as a whole 
and at times as a means of obtaining certain amino acids. If 
such is the case, substantially all the " building stones " of the 
proteins, so far as they cannot be manufactured in the body, 
must be supplied in the feed, but relatively more of certain 
particular ones might be required than would be indicated by 
the make-up of the body proteins. Finally, it seems to be fairly 
well established that at least some of the amino acids can be 
manufactured in the body. This is almost certainly true of 
glycin and perhaps of prolin and arginin. If such be the 
case, it becomes even more clear that the protein requirement, 
so called, is really an amino acid requirement. 

399. Amino acids required for maintenance. — Our actual 
knowledge of the amino acid requirement for maintenance is 
still meager, but it has been shown that a supply of tryptophan 
and probably of tyrosin is necessary for the maintenance of 
nitrogen equilibrium, while lysin is dispensable. 

Willcock and Hopkins, * for example, found that the zein of 
maize, which contains neither tryptophan nor lysin, was capable of 
supporting neither growth nor maintenance in mice, while the addi- 
tion of tryptophan diminished although it did not altogether stop 
the loss of nitrogen from the body. Henriques 2 obtained similar 
although less striking results in experiments with rats. It is to the 
work of Osborne and Mendel 3 that we owe the most conclusive demon- 
stration of the necessity of tryptophan for maintenance. They 
showed conclusively that zein as the sole source of protein was in- 
capable of maintaining rats, while with the addition of tryptophan 
much better results were obtained and in two cases complete main- 
tenance for a long time was secured. Miss Wheeler 4 has reported 
similar results on mice. Furthermore, Osborne and Mendel have shown 
that the deficiencies of zein may be compensated for by the addition 
to the ration of other proteins containing the lacking amino acids. 

1 Jour. Physiol. (London), 35 (1906), 88. 
2 Ztschr. Physiol. Chem., 60 (1909), 108. 

3 Carnegie Institution of Washington, Publication No. 156 (191 1); Jour. Biol. 
Chem., 13 (1912), 233; 17 (1914), 325- 

4 Jour. Exp. Zoology, 15 (1913), 209. 



MAINTENANCE — REQUIREMENTS OF MATTER 315 

On the other hand, they have also shown that lysin is not essential to 
protein maintenance, they having been able to maintain animals for 
long periods on rations containing as their sole protein gliadin, which 
contains no lysin but does contain tryptophan. 

What has been shown regarding the necessity of tryptophan 
and the dispensability of lysin for maintenance may doubtless 
prove to be true for other protein constituents, so that ulti- 
mately it may be possible to estimate the relative maintenance 
values of proteins on the basis of their chemical constitution. 
At present, however, this is far from being the case. The 
constitution of many of the proteins, particularly those of the 
roughages, is known inadequately or not at all, while the specific 
amino acid requirements for maintenance have still to be worked 
out and may conceivably vary as between different species. 

400. Relative values of proteins for maintenance. — The 
facts regarding the variations in the constitution of the different 
proteins which are recorded in Chapter I (50) render it evident 
that these substances may be of quite unequal value as sources 
of amino acids to the organism. Thus, according to the data 
there tabulated, gliadin and zein would be about three or four 
times as valuable as legumin as a source of the amino acid 
prolin, while on the other hand legumin would be 2J times as 
valuable as wheat glutenin as a source of lysin. The cereal 
proteins, especially those of wheat, are notably rich in glutamic 
acid and therefore relatively poorer in other constituents. If, 
then, the protein requirement for maintenance is in reality an 
amino acid requirement it would seem that these various pro- 
teins must be of unequal value for that purpose. 

As regards single proteins, the experimental evidence just 
cited strongly supports this presumption, while Osborne and 
Mendel * have likewise shown the existence of distinct differences 
in the values of lactalbumin, casein edestin, gliadin and milk 
proteins for the maintenance of rats. It must not be forgotten, 
however, that both man and domestic animals ordinarily con- 
sume a mixture of proteins, so that it may be presumed that 
deficiencies or excesses of particular " building stones " com- 
pensate for each other to. a greater or less extent. On the whole 
the statement seems justified that while distinct differences 

1 Jour. Biol. Chem., 22 (1915), 241. 



316 NUTRITION OF FARM ANITvL\LS 

between mixed proteins from different sources as regards their 
value for maintenance have been shown to exist, they appear 
in many cases to be less than might be anticipated from the 
known differences in their chemical constitution. As a matter 
of practical necessity, then, pending the further investigations 
so greatly to be desired, the only course open for the present 
seems to be to follow established custom and deal with the pro- 
tein of feeding stuffs and rations as a whole, with the conscious- 
ness that it is of unequal nutritive value in different materials 
but in the belief that such differences are not in all probability 
so great as to seriously invalidate the general usefulness of the 
results. 



Influence of feed supply on protein katabolism 

401. The minimum of feed protein. — The physiological 
minimum (339) below which the protein katabolism of the 
fasting animal cannot be reduced evidently constitutes a lower 
limit to the necessary supply of feed protein, but what surplus, 
if any, above this minimum must be supplied in order to secure 
actual protein maintenance is still an unsettled question. That 
the amount of feed protein necessary for maintenance is rel- 
atively small has been fully demonstrated. It appears to be 
well established also that on a diet containing an abundance 
of non-nitrogenous nutrients, especially of carbohydrates, a 
supply of protein materially less than the protein katabolism 
during complete fasting is sufficient to meet the needs of the 
organism, while it is possible that an amount little or no greater 
than that katabolized when abundance of carbohydrates is 
consumed will suffice. 

Fats appear to be distinctly less efficient than carbohydrates in 
keeping the protein katabolism at the minimum. Precisely why this 
is the case has not been fully made out, although Landergren l has 
advanced the explanation that a minimum of carbohydrates is essen- 
tial to the chemical processes of metabolism and that when a sufficient 
amount is not supplied in the feed, protein is katabolized for the sake 
of producing carbohydrates, with the result that on a low protein 
diet nitrogen katabolism is increased. 

1 Jahresber. Tier. Chem., 32 (1903), 685. 



MAINTENANCE — REQUIREMENTS OF MATTER 317 

The facts recorded in Chapter VII (335-338), however, make 
it evident that the protein katabolism may be affected by the 
amount of both protein and non-nitrogenous material available 
in the body. For a correct interpretation of the results of ex- 
periments upon the maintenance requirement of protein, there- 
fore, a knowledge of the influence of the feed supply upon the 
protein katabolism is essential. 

402. Surplus protein katabolized. — While a relatively small 
quantity of digestible protein is sufficient, in the presence of an 
abundant supply of fuel material, to maintain the body in 
nitrogen equilibrium, an increase of the feed protein above 
this minimum does not result in any large or long-continued 
gain of protein tissue by the mature animal, but simply in- 
creases the protein katabolism, as is shown by the prompt 
appearance of a corresponding amount of nitrogen in the urine. 



Table 57. — Protein Katabolism of Sheep per Day and Head 





Sheep I 


Sheep II 




Nitrogen 
digested 


Nitrogen 
in urine 


Nitrogen 
digested 


Nitrogen 
in urine 


Period 1 

Period 2 

Period 3 

Period 4 

Period 5 

Period 6 

Period 7 


Grams 

8.18 
17.86 
27.22 

36.99 

26.76 

17.62 

8-34 


Grams 

7.48 
16.82 

25-75 
32.71 

25-63 

16.64 

8.06 


Grams 

7.81 
17.72 

27-33 
37-07 
26.91 
16.94 
8.00 


Grams 

6.98 
16.37 

23-94 
32.09 

24-54 

15-99 

7.62 



The fact was demonstrated more than fifty years ago by C. Voit 
in collaboration at first with Bischoff l and later alone and with Pet- 
tenkofer 2 in experiments on carnivorous animals, and almost innu- 
merable subsequent investigations have shown that it is true not 
only of these animals but of man and of herbivorous animals as well. 

Of the numerous investigations on herbivora in which the nitro- 

1 Gesetze der Ernahrung des Fleischfressers, i860. 

2 Published chiefly in the Annalen der Chemie und Pharmacie and the Zeitschrift 
fur Biologic See also Voit, "Physiologie des Stoffwechsels," in Hermann's Hand- 
buch der Physiologie. 



318 NUTRITION OF FARM ANIMALS 

gen excretion has been determined, Table 57 may serve as an ex- 
ample. 1 Two sheep were fed in periods 1 and 7 a basal ration of 
hay and barley meal. To this ration were added in the intermediate 
periods varying amounts of nearly pure protein in the form of con- 
glutin (of lupins) or of flesh meal. A comparison of the nitrogen 
digested from the ration with the urinary nitrogen shows that the 
latter increased and diminished substantially parallel with the former. 

403. Utilization of protein limited. — That the mere consump- 
tion of protein cannot cause a large storing up of it is indeed 
sufficiently obvious from daily experience. The muscles of 
the weakling cannot be converted into those of the athlete by 
feeding him upon a meat diet, nor the small man increased in 
size by a very abundant protein supply. The protein tissues 
of the mature animal have reached their natural limit of size 
and consequently the capacity of the body to store up protein 
is limited. Beyond the minimum required to make good the 
necessary katabolism in the cells, protein can be utilized in 
such an animal only to a small extent as protein, and it is there- 
fore rapidly katabolized, its nitrogen appearing in the urine as 
urea and other familiar end products. Nor is the situation 
essentially different in the growing or the milk-producing 
animal. While these animals are able to utilize consid- 
erable amounts of feed protein, yet the limit to this utilization 
is set by the normal rate of growth of the protein tissues or 
the capacity of the mammary glands to manufacture the 
casein and other proteins of the milk. Any surplus of pro- 
tein over what can be used for this purpose is katabolized 
precisely as is a surplus over the very small demand of the 
unproductive mature animal. (Compare Chapter XI, § 2 and 
Chapter XIII, § 4.) 

404. Protein as a source of energy. — This increased katab- 
olism of protein, however, is not to be regarded as the total 
loss of so much feed material. In the presence of a surplus of 
protein, the amino acids resulting from its digestion are in 
large part deaminized (233), their nitrogen being excreted 
chiefly as urea, while a non-nitrogenous residue is left which 
contains the larger portion of the chemical energy of the protein 
which it represents and is in condition to be oxidized as fuel 

1 Henneberg and Pfeiffer; Jour. Landw., 38 (1890), 215. 



MAINTENANCE — REQUIREMENTS OF MATTER 319 

material (229). The increased nitrogen excretion on a high 
protein diet is simply the method by which the organism gets 
rid of surplus nitrogen while retaining the larger share of the 
energy of the protein for fuel purposes. It does not mean the 
total destruction of the corresponding amount of protein, but 
simply its transformation into compounds which can serve as 
sources of energy. 

405. Fluctuations of body protein. — Although in the mature 
animal a surplus of feed protein is largely katabolized, so that 
a continued increase of the protein tissue of the animal cannot 
be brought about, as can that of the adipose tissue, simply by 
a surplus in the feed, the protein content of such an animal is 
not to be regarded as absolutely fixed, so that the protein supply 
has no effect upon it. On the contrary, a considerable range of 
variation is possible. 

Thus it is a familiar fact that a fasting animal may live and 
continue to perform the essential bodily functions for some 
time while losing daily a not inconsiderable amount of protein. 
To cite a single striking example, Rubner observed in a fasting 
rabbit up to the time of death, on the nineteenth day, a loss of 
45.2 per cent of trie computed nitrogen of the body. While 
this is an extreme instance, nevertheless it is evident that there 
must be a relatively large loss of body protein in those more mod- 
erate cases in which the deprivation of protein is not continued so 
long as to cause death. Furthermore, the losses occurring in 
these latter cases may be made good by subsequent feeding 
and the animal restored to its original state. Illustrations of 
the same fact are familiar in the human subject in the emacia- 
tion due to illness and the restoration of the body during con- 
valescence. In brief, it is evident that the body of the mature 
animal may fluctuate within somewhat wide limits as regards 
its protein content without necessarily causing any serious or 
permanent derangement of its functions. 

406. Storage of feed protein. — Similar, although smaller, 
fluctuations in the protein content of the body appear to be 
caused by variations in the supply of feed protein, an increase 
in the latter giving rise to more or less storage of nitrogenous 
matter in the body, while a decrease has a contrary effect. 

In other words, as regards its stock of nitrogenous materials 
the organism may exist and function at a higher or lower level 



320 NUTRITION OF FARM ANIMALS 

according to the amount of protein supplied in the feed, while 
for each level of protein stock a certain supply in the feed is 
necessary — that is, the protein requirement for maintenance 
varies. With carnivora on a largely protein diet the adjust- 
ment of the body to the protein supply seems to take place 
rather promptly. In the case of herbivora, however, the ad- 
justment appears to be more gradual, possibly owing to the 
relatively large supply of non-nitrogenous ingredients in their 
feed, and apparently some gain of protein may continue for a 
considerable time, although when expressed as a percentage of 
either the total feed protein or of the body protein the gain is 
relatively small. 

407. Effect of deficiency of non-nitrogenous nutrients. — 
The prime demand of the organism is for energy for the per- 
formance of its vital functions, and if necessary it will draw 
upon its own tissues for this purpose. No clear conception of 
the laws of protein metabolism can be reached without taking 
into consideration the energy relations. 

As has already been shown, the proteins or at least the cleavage 
products of their digestion readily undergo a process of deam- 
inization by which their nitrogen is split off and excreted, leaving 
a non-nitrogenous residue which is available as a source of 
energy. Ordinarily, however, the proportion of energy derived 
from the katabolism of protein is relatively small, the non- 
nitrogenous nutrients constituting its principal source. 

But if, with an amount of protein in the feed just sufficient 
to sustain nitrogen equilibrium, the non-nitrogenous nutrients, 
especially the carbohydrates, be so reduced in amount that 
the total energy supply is insufficient for maintenance, not 
only is body fat drawn upon to make up the deficit, but the 
protein katabolism also increases, so that a supply of this 
nutrient which was previously adequate became insufficient 
and a loss of body protein occurs. 

The effect is naturally most marked when the non-nitrogenous 
nutrients are withdrawn altogether. For example, Voit and Korku- 
noff x found that when a dog was given an abundant supply of carbohy- 
drates, protein equivalent to about 4.5 grams of nitrogen was sufficient 
to maintain him in nitrogen equilibrium. But when a similar amount 

^tschr. Biol., 32 (1895), 67. 



MAINTENANCE — REQUIREMENTS OF MATTER 32 1 

of protein was given without non-nitrogenous nutrients it proved 
entirely insufficient for this purpose and about three times as much 
was required to attain protein maintenance, as the following table 
shows : — 

Table 58. — Effect of Protein Supply on Protein Katabolism of 

Dog 



Feed 



Nothing 

Extracted meat (grams) 

100 

140 

165 

185 

200 

230 

360 ...... . 

410 

360 





Nitrogen in — 




Feed 


Feces and 


Gain ( + ) or 


urine 


loss ( — ) 


Grams 


Grams 


Grams 


O 


3-9Q6 


- 3-996 


4.10 


5-558 


- 1-458 


5-74 


6-495 


- -755 


6.77 


7.217 


- -447 


7-59 


7.804 


— .214 


8.20 


8.726 


- .526 


10.24 


IO-579 


- -339 


11.99 


12.052 


— .062 


15.58 


14.314 


+ 1.266 


13-68 


13.622 


+ .058 



The results furnish also a striking illustration of the interesting rela- 
tions between protein supply and protein katabolism which had been 
demonstrated more than 30 years earlier by the classic experiments 
of BischorT and Voit (402), while rendering it evident that the quantity 
of protein required to produce nitrogen equilibrium when fed alone is 
very far from representing the minimum demand of the body. 

What is so strikingly true in the total absence of non-nitrog- 
enous nutrients holds good also in less degree in case of their 
relative deficiency. If a portion of the non-nitrogenous nu- 
trients are withdrawn from a mixed ration, the protein katab- 
olism usually increases. 

408. Effect of surplus of non-nitrogenous nutrients. — If, 
on the contrary, non-nitrogenous nutrients be added to a 
ration, they tend to diminish the katabolism of protein. 

As regards rations deficient in energy, this is, of course, only 
the converse of the statement of the preceding paragraph that 



322 



NUTRITION OF FARM ANIMALS 



the withdrawal of these materials tends to increase the protein 
katabolism, and as regards maintenance or submaintenance 
rations the two statements are equivalent. But even in the 
case of supermaintenance rations it has been found that the 
addition of a surplus of fat or, in particular, of carbohydrates, 
to a ration containing more than the minimum of protein tends 
to reduce the protein katabolism to a lower level. The effect 
is well illustrated, for example, by those of Kellner's respiration 
experiments on cattle l in which starch was added to basal 
rations which were themselves sufficient to cause some fattening. 
The following table compares the urinary nitrogen upon the 
basal ration with that upon the augmented ration : — 

Table 59. — Effect of Starch on Protein Katabolism of Cattle 



OxD 
OxF 
OxG 
OxH 
Ox J 



Daily Urinary Nitrogen 



On basal 


With addition 


ration 


of starch 


Grams 


Grams 


122.54 


104.69 


106.03 


81.18 


86.30 


63-83 


109.28 


81.71 


122.62 


103.13 



It has likewise been shown that this effect is produced not 
only by the true fats and by the soluble hexose carbohydrates, 
such as starch and the sugars, but likewise by the pentoses and, 
in the case of herbivorous animals, by those ill-known ingredients 
of feeding stuffs, especially of the crude fiber and the nitrogen- 
free extract, which disappear in the passage of the feed through 
the alimentary canal and which are commonly spoken of as 
being digested. This statement covers also the organic acids, 
whether resulting from the fermentation of the carbohydrates 
or contained in the feed. 

409. Protein katabolism depends chiefly on supply. — It 
should be clearly understood that even in the presence of a 
surplus of fat or carbohydrates the dependence of the protein 
1 Landw. Vers. Stat., 53 (1900). 



MAINTENANCE — REQUIREMENTS OF MATTER 323 

katabolism upon the protein supply still holds true. Even 
the most liberal supply of non-nitrogenous nutrients cannot 
prevent the splitting-off and excretion of the nitrogen of surplus 
protein which was illustrated in previous paragraphs, but simply 
reduces it somewhat below the level which it would otherwise 
reach. To that extent, it helps to bring about, and probably 
to prolong somewhat, the temporary storage of protein men- 
tioned on a previous page (406) and thus to bring the animal 
upon a higher plane of protein nutrition. 

It is clear from the foregoing statements that no sharp dis- 
tinction is to be conceived of between an insufficiency and a 
sufficiency of non-nitrogenous nutrients, but rather a tendency 
on the part of the latter to diminish the protein katabolism, a 
tendency more or less marked according to their abundance in 
the ration. It is not to be understood that no nitrogenous 
material is katabolized for fuel purposes as long as sufficient 
non-nitrogenous nutrients are present to supply the demands 
for energy, nor that even the largest quantities of the latter 
can prevent the katabolism of protein supplied in excess of its 
possible constructive use by the body. 

Protein requirements of farm animals 

410. Minimum and optimum of protein. — In considering the 
protein requirements of the different species of farm animals, 
it is important to distinguish between two points of view. On 
the one hand, it may be sought to determine the least amount 
of feed protein upon which the protein tissues of the animal can 
be maintained. On the other hand, the endeavor may be to 
formulate the most advantageous amount of protein to supply 
when an animal is actually to be maintained for a time and this 
amount may very possibly be greater than the physiological 
minimum. The first point of view, however, is plainly the 
fundamental one and should first receive consideration. Hav- 
ing determined the lower limit of protein supply, it will then 
be possible to consider intelligently the advantages, if any, of 
a surplus. 

In considering the results of experiments directed toward the 
determination of the minimum of feed protein required by any 
individual or species, it is essential to bear in mind the facts 



324 NUTRITION OF FARM ANIMALS 

regarding the influence of the feed supply upon the protein 
katabolism which have just been considered. 

411. The plane of protein nutrition. — It has been shown 
in previous paragraphs that the protein katabolism adjusts 
itself more or less promptly to the supply in the feed. A surplus 
above the minimum requirement, while causing a small storage 
of protein, results chiefly in raising the plane of protein nutrition 
and so increasing the katabolism until income and outgo of 
nitrogen come into equilibrium. The mere fact, therefore, 
that an animal is in equilibrium with a certain supply of protein 
in its feed by no means proves the latter to be the least amount 
necessary for the maintenance of the animal, since it may be 
living upon an unnecessarily high plane of protein nutrition. 

412. The supply of non-nitrogenous nutrients. — It has 
also been shown that the sufficiency of a given amount of pro- 
tein depends not only upon the plane of protein nutrition of 
the body, but also, within certain limits, upon the amount of 
non-nitrogenous nutrients supplied with the protein. With 
an abundant supply of the former an amount of protein equal to 
the fasting katabolism, or perhaps even less, appears to be a 
sufficient minimum for maintenance. As the supply of non- 
nitrogenous materials is reduced a larger supply of feed protein 
seems to be required to reach equilibrium because more and 
more of it is diverted for use as fuel, so that in the total absence 
of non-nitrogenous nutrients a large excess of protein must 
be fed before equilibrium between income and outgo of nitro- 
gen is reached. In interpreting experiments or formulating a 
maintenance ration, therefore, it is not sufficient to consider 
simply the amount of protein, but account must also be taken of 
the supply of non-nitrogenous materials, and only when the 
net energy content of the ration is ample for maintenance can 
it be concluded that a loss of body protein shows the protein 
supply to be insufficient. 

413. Value of non-protein. — The crude protein of the feed 
of farm animals includes not only true protein but a great 
variety of other nitrogenous substances, grouped for con- 
venience under the designation non-protein. In considering 
the results of experiments upon the protein requirements of 
these animals, therefore, it is necessary to determine whether 
the true protein should be the basis of comparison or whether 



MAINTENANCE — REQUIREMENTS OF MATTER 325 

the non-protein has some value for maintaining the protein 
tissues of the body. 

It appears to have been demonstrated by recent experimental 
results, especially by those of Kellner, Morgen, and the Labora- 
tory for Agricultural Research in Copenhagen, that the non- 
protein of ordinary feeding stuffs is available for the maintenance 
of ruminants, probably indirectly through a conversion to 
protein by means of micro-organisms in the digestive tract 
(141). On the other hand, investigations have thus far failed 
to demonstrate that non-protein has any material value for 
other species or for production purposes (786-789). In the 
computation of rations for productive feeding, therefore, it 
appears desirable for the present to consider ordinarily only 
the digestible true protein, ignoring the non-protein. This 
implies, however, that the results of experiments upon the 
protein requirement shall be expressed in the same manner. 

This will have two effects : First, it will make the protein require- 
ment appear smaller than it really is. Suppose, for example, that 
a series of trials in which the ratio of digestible non-protein to 
digestible protein is 1 : 10 shows that nitrogen equilibrium is reached 
with a ration supplying 500 grams protein and 50 grams non- 
protein. Regarding the true protein only, the maintenance require- 
ment is 500 grams, while including the non-protein it is 550 grams. 

In the second place, however, this error will be largely compen- 
sated for when the actual computation of rations is also based on the 
true protein. Thus in the case just supposed, if a maintenance ration 
be computed from any feed or mixture in which the ratio of non- 
protein to protein is the same as in the experiments from which the 
maintenance was deduced, viz., 1 : 10, it is obvious that the same final 
result will be reached whether the maintenance requirement be con- 
sidered to be 500 grams of true protein or 550 grams of crude protein. 
Only when the proportion of non-protein to true protein varies widely 
from that existing in the rations used in determining the protein re- 
quirement will any significant error arise in computing rations. 

In the results considered on succeeding pages, both the crude 
protein and true protein of the rations are stated when these 
are given in the reports of the experiments. 

414. Computation to unit weight. — It was shown in Chap- 
ter VII (345) that the energy requirement for maintenance is 
substantially proportional to the body surface of the animal. 



326 NUTRITION OF FARM ANIMALS 

No similar comparisons of the protein requirement appear to 
have been made. Since, however, the minimum protein re- 
quirement does not represent a demand for energy but for 
certain specific substances required for the normal functioning 
of the body, it seems plausible to suppose that its amount will 
depend rather upon the mass of active tissue than upon the body 
surface. If such be the case, the protein requirement may, 
with sufficient accuracy for practical purposes, be computed in 
proportion to the live weight and that course is followed in 
the succeeding paragraphs. 

415. Protein requirement of cattle. — For obvious reasons 
it is impracticable to ascertain the fasting katabolism of rumi- 
nants as a basis for estimating their maintenance requirement 
as regards protein, but by a comparison of the recorded experi- 
ments in which the nitrogen balance upon small amounts of feed 
has been determined it is possible to fix approximately the limit 
of protein supply below which, even in the presence of an abun- 
dant supply of non-nitrogenous nutrients, a loss of body protein 
occurs. 

Of the investigations upon the energy requirement for main- 
tenance summarized in Chapter VIII (381) only those of Kellner 
and the live weight experiments of the writer, together with 
the early results of Henneberg and Stohmann, afford data 
regarding the minimum protein requirement. While protein 
maintenance was probably secured in the remaining instances 
there is no sufficient evidence to show that a surplus of protein 
was not being consumed (402, 411). In addition to the foregoing, 
the investigations by the Laboratory for Agricultural Research 
in Copenhagen 1 upon the protein requirements for milk pro- 
duction (586) also afford approximate data as to the main- 
tenance requirement, and Fingerling, 2 in experiments upon the 
protein requirements of growing calves (471), obtained inter- 
esting indications regarding the quantity required for main- 
tenance. 

The lowest recorded amounts per 1000 pounds live weight 
upon which nitrogen equilibrium was reached were 0.21 pound 

1 Denmark-Beretning fra den Kgl. Veterinaer of Landbohojskoles Laboratorium 
for landokonomiske Forsog. 6ode, 1906, and 63de, 1907, Kobenhavn. Translated 
by Mallevre, Societe de l'Alimentation Rationelle du Betail. Compte Rendu de 
1 1 erne et i2eme Congres. 

2 Landw. Vers. Stat., 76 (1911), 1. 



MAINTENANCE -REQUIREMENTS OF MATTER 327 

and 0.25 pound of crude protein in experiments on dry cows 
while in experiments on steers almost as small a quantity viz 

nnl P T? T . Pr ° tein ° r °- 23 P ° Und true P rot ^, fell very" 
httle short of maintaining the nitrogen balance. Aside from 

these somewhat exceptional results, the lowest figures obtained 
were . 43 pound de ^^ and 

If the few exceptionally low figures be omitted, the average and 
range of the results of the other experiments are as follows - 



Table 60. -Average and Range op Protein Requirement of Cattle 




It seems safe, therefore, to estimate 0.6 pound of crude pro- 
tein or 0.5 pound true protein per 1000 pounds live weighi as 
representing m a general way the minimum protein require- 
ment of cattle, with a range of perhaps 0.1 or o 2 pound either 
way under varying conditions. 

416. Protein requirement of sheep. - While a considerable 
number of experiments with sheep are on record in which live 
weight maintenance was secured, and a smaller number in which 
the nitrogen balance was maintained, few of them afford satis- 
factory data as to the minimum protein requirement. 

A distinct difference between cattle and sheep, which affects the 
proton requirement, lies in the greater demand fir protein in dent 

^l S T< ° f W ° 0l ; n the la " er anima ' S as C0 « with thaTo 
hair in the former. Determinations by Armsby and Fries on the 

same two steers in two consecutive winters showed an average pro! 
duction of epidermal tissue, including the growth of hair and the kss 
m brush.ngs, equivalent to 0.0025 lb. protein per day and ™ 
pounds live weight, an amount too small to materially affect the main- 
tenance requirement. In the case of sheep, determinations by seve al 
nvestigators have shown the daily growth of wool per 1000 pounds 
live weight to contain from 0.10 to 0.15 lb. of protein, the average 
being 0.135 lb. Although, as these figures show, the protein re- 



328 NUTRITION OF FARM ANIMALS 

quirement of sheep for the growth of wool is considerably greater than 
that of cattle for the growth of hair, the absolute difference, after all, 
does not add very greatly to the total maintenance requirement. 

The current feeding standards for the maintenance of sheep call 
for 1. 0-1.6 lb. of digestible crude protein per 1000 pounds live 
weight, apparently upon the basis of Henneberg and Stohmann's early 
experiments (382) in which 1.3 lb. of crude protein or 1.041b. true 
protein produced but a slight gain of body protein in addition to the 
growth of the wool. There can be little doubt, however, that Henne- 
berg and Stohmann's sheep received a surplus of protein above the 
actual maintenance requirement. 

In a series of 20 digestion and metabolism experiments by Schulze 
and Marcker, 1 decidedly smaller amounts of protein proved sufficient 
to maintain nitrogen equilibrium, the average of 6 experiments in 
which no loss of body protein was observed being 0.653 lb. digest- 
ible crude protein per 1000 pounds live weight. It is evident, then, 
that the protein supply of sheep can be reduced much below the 
amount fed in Henneberg and Stohmann's experiments without lead- 
ing to a loss of body protein. 

The most satisfactory data regarding the minimum require- 
ment of sheep are afforded by Katayama's 2 investigations, in 
which increasing amounts of nearly pure protein (" aleuronat ") 
were added to a basal ration very poor in protein, consisting of 
hay, oat straw, starch and cane sugar. The protein in every case 
was substituted for a corresponding amount of starch, so that 
the total energy of the ration remained substantially unchanged. 
On the average of two animals, 0.41 lb. digestible true protein 
per 1000 pounds live weight was sufficient to maintain the 
nitrogen balance. Since, however, the growth of wool must 
have gone on, with a corresponding storage of nitrogen, there 
must have been an equivalent loss of protein by the active 
tissues of the body. 

If to the minimum of 0.41 pound there be added 0.14 lb. 
per 1000 pounds live weight for the growth of wool, it appears 
that the minimum protein requirement for the maintenance of 
mature sheep is in the neighborhood of 0.55 lb. It is inter- 
esting to note that the actual maintenance requirement for 
the body tissues is apparently quite as low relatively as for 
cattle. 

1 Wolff ; Die Ernahrung der landwirtschaftlichen Nutztiere, p. 300, 

2 Landw. Vers. Stat., 69 (1908), 321. 



MAINTENANCE — REQUIREMENTS OF MATTER 329 

417. Protein requirement of swine. — The determinations 
of the fasting katabolism of swine recorded in Chapter VIII 
(377) gave an average of 0.48 lb. per thousand pounds live 
weight for the fasting protein katabolism of swine, although 
with a considerable range in the individual results. McCollum l 
has reported considerably lower figures for the protein katab- 
olism of swine receiving no protein but fed liberal amounts of 
starch, the mean of twelve experiments being 0.26 lb. per 
1000 pounds live weight with a range of 0.14 lb. -0.33 lb. 
Whether, however, such small amounts as these are sufficient 
for actual maintenance, or if not, what excess above them is 
necessary, has not been certainly determined. 

In the experiments of Von d. Heide and Klein (378), in one of 
which an approximate maintenance ration was fed to three young 
swine, there was a material gain of protein by the animals. The 
amounts actually katabolized, however, as shown by the amount of ni- 
trogen excreted in the urine, were as follows for the three animals- 
together : — 





Total Live 
Weight 


Protein Katabolism 




Per Head 


Per 1000 Lb. 
Live Weight 


Period I Maintenance 

Period III Fattening 


Kgs. 

228.1 
246.5 
261.5 


Grams 

152.4 
156.2 
I5I-3 


Lb. 

0.67 
0.63 
0.58 



Dietrich, 2 in his experiments upon maintenance ration of swine 
(378), found that 0.70 to 0.84 lb. of digestible protein per thousand 
pounds live weight sufficed to produce nitrogen equilibrium in two 
periods following an eight-day fasting period, but that about the same 
amounts (0.80 to 0.90) previous to the fasting period were insufficient, 
while in two trials in which respectively 0.94 and 1 .06 lb. were con- 
sumed protein maintenance was reached. 

418. Protein requirement of the horse. — In the experiments 
by Grandeau and LeClerc described in Chapter VIII (386 d), 

1 Wis. Expt. Sta., Research Bui. 21. 

2 Ills. Expt. Sta., Bui. 163 (1913). 



33° 



NUTRITION OF FARM ANIMALS 



the nitrogen balance of the horses was determined during six 
of the periods. The following table shows the amounts of 
protein and of non-protein nitrogen digested in each period, 
the urinary nitrogen, and the small losses in epithelial tissue 
(epidermis, hoofs, hair, etc.) : — 

Table 6i. — Nitrogen Balance of Horses 





Horse 


No. 1 


Horse 


No. 2 


Horse No. 3 




January, 
1884 


April, 
1884 


Novem- 
ber, 1883 


Mav, 
1884 


December, 
1883 


March, 

1884 


Digested : 

Protein nitrogen . 
Non-protein 

nitrogen . . 


Grams 
43-19 

1.20 


Grams 
34-29 

— I.OI 


Grams 
38.94 

- 3-23 


Grams 
34.22 

10.78 


Grams 
41.82 

— 2.09 


Grams 
24.72 

- 4.58 


Total nitrogen 


44-39 


33-28 


35-71 


35 -oo 


39-73 


20.14 


Nitrogen of epithe- 
lial tissue 
Urinary nitrogen . 
Nitrogen gained 


1.46 

35-17 
7.76 


1.46 

38.75 

- 6.93 


I.46 

30.70 
3-55 


1.46 

41.92 

1.62 


1.46 

37.62 

0.65 


I.46 

32.70 
— 14.02 



Omitting the results upon horse No. 3 in March, when the 
digestible protein was exceptionally low, the other five periods 
show an average daily gain of nitrogen of 1.33 grams, while 
the average crude protein digested was 235 grams, or 0.59 
,1b. per 1000 pounds live weight, equivalent to about 0.50 lb. 
true protein. 

419. The optimum of protein. — The data of the foregoing para- 
graphs seem to indicate a striking uniformity in the minimum 
protein requirement of the principal species of domestic animals 
with perhaps the exception of the hog when mature, 0.4 to 0.6 
lb. per 1000 pounds live weight apparently sufficing to main- 
tain nitrogen equilibrium under favorable conditions. 

It should be clearly understood, however, that this figure 
represents a more or less accurately determined limit. It pur- 
ports to be the amount below which the protein supply can- 
not be reduced without eventual protein starvation. The 
animal body, however, may adjust itself to a wide range of 
protein supply above the minimum, using some of it to increase 



MAINTENANCE — REQUIREMENTS OF MATTER 331 

the stock of protein in the body and katabolizing the remainder 
as fuel material. An increase of the protein supply above the 
minimum causes, after a relatively short time, the main- 
tenance of the body protein at a higher level (411). The prac- 
tical question in actual maintenance is far less as to the least 
amount of protein which may be used than as to the most 
advantageous level of protein nutrition; that is, as to the 
optimum of protein. 

This question has been warmly debated in connection with 
human nutrition, having been brought to the fore especially 
by the investigations of Chittenden and his associates. 1 

On the whole it cannot be said that a considerable surplus 
of protein over the minimum requirement for maintenance — 
that is, the maintenance of protein nutrition on a high plane 
— has been proved to be of any material advantage in the 
maintenance either of men or of domestic animals during 
periods covering several months. Whether a continued low 
protein diet through years or generations would show a different 
result is at present largely a matter of speculation. It is to be 
remarked, however, that the particular point under discussion 
is the protein requirement of the mature organism. That a 
deficiency of protein in the diet of a growing animal may have 
disastrous results is clear. If, however, the habitual food supply 
of a race of men or a group of animals is low in protein, the 
young are likely to share this deficiency with the mature, and 
it seems not impossible that this is an important factor in the 
alleged physical inferiority of certain races of men living on a 
low protein diet. This consideration warns us to exercise care 
in this respect in the management of the breeding herd. 

420. Digestibility of low protein rations. — In the actual 
maintenance feeding of farm animals, the matter of the digest- 
ibility of the ration must also be considered. It has been 
shown (723, 724) that a relative deficiency of protein in the 
ration tends to depress the apparent digestibility of both the 
protein and non-nitrogenous nutrients, especially in the case of 
ruminants. A maintenance ration for these animals containing 
the minimum amount of protein together with the quantity 
of non-nitrogenous nutrients required to maintain the energy 
supply, would have a nutritive ratio (709) , computed in the ordi- 

1 Physiological Economy in Nutrition. 



332 NUTRITION OF FARM ANIMALS 

nary way, of approximately i': 12. On such a ration there 
would, in all probability, be some loss of digestibility and an in- 
crease of its protein by 50 per cent might perhaps effect a gain in 
digestibility which would more than offset the increased cost, 
if any. Indeed, unless feeding stuffs especially poor in protein 
are used, it may often be difficult, even were it desirable, to 
reduce the protein content of a maintenance ration to the low 
level of absolute necessity. 



§ 2. The Ash Requirements for Maintenance 

421. Ash ingredients indispensable. — That a supply of 
the so-called mineral or ash ingredients, as well as of protein 
and of energy yielding materials, is necessary for the growth and 
maintenance of animals has been fully recognized since the 
time of Liebig, and was strikingly demonstrated by the well- 
known experiments of Forster * and of Lunin, 2 which showed 
that animals supplied only with ash-free feed perished even 
sooner than when deprived of all feed. 

Some of the reasons for these facts were indicated in the dis- 
cussion of the functions of the nutrients in Chapter V (268-272), 
where it was shown that, besides their structural importance 
for both the skeleton and the soft tissues, the presence of ash 
ingredients in the body fluids is essential to the maintenance 
and regulation of the vital processes. Aside from the specific 
uses of single elements, such as iron, fluorin, iodin, etc., three 
general functions of the ash ingredients as a whole were there 
mentioned, viz., the maintenance in the body fluids and tissues 
of the normal osmotic pressure and of the relative concen- 
tration of the various ions, and, as a specific case of the latter, 
the preservation of neutrality. 

422. Ash content of feed large. — Most feeding stuffs, how- 
ever, and particularly the mixed rations of farm animals, con- 
tain what appear at first sight to be much larger amounts of 
ash ingredients than the body requires. Milk production, for 
example, causes an exceptionally large drain upon the ash 
content of the body, yet even rations made up of materials 
relatively poor in ash contain much larger amounts than are 

1 Ztschr. Biol., 9 (1873), 297. * Ztschr. Physiol. Chem., 5 (1881), 31. 



MAINTENANCE — REQUIREMENTS OF MATTER 333 

found in the milk produced. Zuntz ! gives the following com- 
parison of the ash ingredients in a ration recommended by 
Kellner for a cow producing 22 pounds of milk daily with the 
ash content of the milk yield : — 

Table 62. — Comparison of Ash Content of Ration and of Milk 





CaO 


MgO 


K2O 


Na 2 


P2O5 


CI 




Grams 


Grams 


Grams 


Grams 


Grams 


Grams 


In ration 














88 lb. wet distiller's grain . 


12 


24 


120 


20 


52 


8 


5.5 lb. meadow hay . . . 


17 


8 


43 


2 


9 


17 


8.8 lb. straw 


10 


3 


30 


3 


8 


5 


4.4 lb. dried potatoes . . 


2 


4 


45 


1 


9 


3 


1.1 lb. wheat bran . . . 


7 


3 


6 


0.2 


11 


o.5 


2.2 lb. sesame cake . . . 


25 


13 


H 


4 


32 


1 




73 


55 


258 


30.2 


121 


34-5 


In 22 lb. milk 


17 


2 


17 


4 


20 


10 



Comparisons like the foregoing have tended to confirm the 
somewhat prevalent idea that rations adequate in other re- 
spects may be assumed to contain a sufficiency of ash ingredients. 
This is doubtless true of animals living in a state of nature but 
it is a questionable assumption under the artificial conditions 
to which many farm animals are subjected, as when receiving 
an excess of some single grain like Indian corn or of technical 
by-products, or when stimulated to a high degree of produc- 
tion. 

423. Ash ingredients digestible. — It is true that of this rela- 
tively large supply of mineral matter in ordinary rations, a very 
considerable fraction, especially of certain elements, is found 
in the feces, and this fact has led to their being regarded as 
relatively indigestible. As was stated in Chapters III and 
IV (164, 199), however, this apparently low digestibility arises 
from the fact that the intestinal tract constitutes the normal 
path of excretion for certain elements, notably, in the case of 
herbivora, for calcium and phosphorus. Thus Forster has 
shown that in the dog the calcium of the feed is largely resorbed 

1 Jahrb. Deut. Landw. Gesell., 1912, p 570. 



334 NUTRITION OF FARM ANIMALS 

in the upper part of the intestine where the contents are acid, 
while more or less of it is excreted again in the lower intestine. 
While it is impossible, therefore, to determine by means of the 
ordinary digestion experiment how much of such ingredients 
have actually been resorbed and excreted again and what 
proportion has escaped digestion, it appears safe to conclude 
that at least a considerable share of them has been dissolved and 
resorbed in the upper digestive tract and that the insufficiency 
of certain rations as regards mineral ingredients is not due to 
the indigestibility of the latter. 

424. Contrast between organic and inorganic nutrients. — 
There is an obvious distinction between organic and inorganic 
nutrients. The former may be said to be destroyed in the 
performance of their functions. A molecule of dextrose or of 
stearin, for example, can yield energy to the body only by being 
split up and oxidized step by step to carbon dioxid and water. 
The case is similar with protein so far as it is used for fuel pur- 
poses and even its specific functions seem to involve the cleavage 
and oxidation of its molecules. With the electrolytes contained 
in the body the case is different. A molecule of disodium 
phosphate, for example (or its ions), is not destroyed by the 
performance of its functions in maintaining neutrality no matter 
how long it serves that purpose and the molecule of sodium 
chlorid contributes its quota to the osmotic pressure of the 
blood serum as long as it remains dissolved in that fluid. Only 
as it escapes from the body will the need for a fresh supply 
arise. 

Losses of ash 

425. Causes of loss. — So far, therefore, as the maintenance 
of mature animals is concerned, the magnitude of the ash re- 
quirement will be substantially determined by the rate at 
which the various elements are eliminated from the body 
through the excretory organs. In growing animals there is in 
addition, of course, the demand for ash ingredients for structural 
purposes, both for the building up of the skeleton and to a less 
degree of the soft tissues, but even in this case the total ash 
requirement is determined in large degree by the rate of ex- 
cretion. 



MAINTENANCE — REQUIREMENTS OF MATTER 335 

Some of the more important factors leading to the excretion 
of ash ingredients from the body and hence to the depletion of 
its stock are considered in the following paragraphs : — 

426. Maintenance of osmotic pressure. — In the discussion 
of excretion in Chapter IV it was stated (198) that the essential 
function of the kidneys is to maintain a constant composition 
of the blood, those organs acting somewhat like an overflow 
valve by means of which any excess of a substance above the 
normal limit begins to be excreted. In this way the osmotic 
pressure in the body is regulated and an excess of any salt in 
the feed, sodium chlorid for example, is disposed of. 

The matter is not quite so simple, however, as would appear 
from the foregoing statement. The action of the kidneys in 
eliminating surplus salts and so preventing an increase of osmotic 
pressure is not confined to the particular salt supplied in excess 
but extends to others also. This is most strikingly shown in 
the case of the alkalies. If, for example, unusual amounts 
ot potassium salts are consumed, an increased excretion of 
this element results in the urine, but the need of keeping 
the osmotic pressure at its normal level seems to be so great 
that more or less of the sodium salts are also excreted, even 
though their concentration in the blood may not be above the 
normal. 

This relation as regards potassium and sodium has been 
shown by the well-known investigations of Bunge, 1 who holds 
that the desire for common salt on the part of herbivora is due 
to the presence of relatively large amounts of potassium in 
their feed and the consequent tendency towards impoverish- 
ment of the body as regards sodium. The occurrence of salt 
hunger in animals receiving feed with an abnormal ratio of 
potassium to sodium has been explained in the same way 

In other words, the effort of the body to maintain the osmotic 
pressure of its fluids by removing a surplus of some one ingre- 
dient may bring about an impoverishment as regards other 
elements and so create a need for an increased supply of the 
latter in the feed. 

427. Maintenance of neutrality. — Attention was called in 
Chapter V (271) to the fact that practical neutrality of the 
blood serum and lymph is necessary for the normal functioning 

1 Physiologie des Menschen, 1905. 



336 NUTRITION OF FARM ANIMALS 

of the body cells and to the important part played by the ash 
ingredients in maintaining this neutrality. 

a. Acidosis. — A variety of chemical processes, both normal 
and pathological, occur in the body which tend to disturb its 
neutrality either by the addition of acid or the giving off of 
alkali so as to produce the condition known as acidosis, by 
which is meant a relative excess of acid over basic radicles. 

A well-known example of pathological acidosis is that observed in 
diabetes. The perverted metabolism of this disease results in the 
production of large amounts of oxybutyric acid (266), which is neu- 
tralized to a certain extent by means of ammonia derived from the 
katabolism of protein but whose gradual accumulation finally results 
in the diabetic coma. Another example is the form of infantile aci- 
dosis in which an excess of fat in the food results in the formation of 
insoluble calcium salts of the fatty acids in the intestines and so re- 
moves basic ingredients in the feces. It has been suggested that the 
failure of young animals to thrive on milk exceptionally rich in fat 
may be due in part to the same cause. 

Several sources of acid exist in the normal organism. 

First, acids may be consumed as such, either in natural 
products or in fermented materials like silage. These acids 
are neutralized by the alkalies of the saliva or of the pancreatic 
juice, which are thus temporarily withdrawn from the body 
fluids. After resorption, however, the resulting alkali salts of 
the more common acids are readily oxidized, yielding carbon 
dioxid and water and restoring to the body fluids the bases 
previously withdrawn. Small amounts of some acids, such as 
tartaric and malic, however, tend to escape oxidization and to be 
excreted in the urine, carrying a corresponding amount of base 
with them. Oxalic acid and its salts are oxidized with difficulty 
and tend to impoverish the body in calcium by the formation 
of the insoluble calcium oxalate. This acid is liable to be es- 
pecially injurious to horses and swine and to young ruminants, 
while in mature ruminants it seems to be largely destroyed by 
fermentation in the first stomach. 

Second, the fermentations in the paunch of ruminants are a 
source of large amounts of organic acids which, like those con- 
tained in the feed, may cause a temporary withdrawal from the 
body fluids of alkali which is later restored when the salts are 
katabolized. 



MAINTENANCE — REQUIREMENTS OF MATTER 337 

Third, the considerable amount of hippuric acid produced 
by herbivora makes a very considerable draft upon the organism 
for bases. Thus, in four experiments by Diakow cited by 
Zuntz, it was equivalent to from J to | of the total excess of 
bases over inorganic acids in the urine. 

Fourth, in the katabolism of the proteins, nucleo-proteins 
and other compounds containing sulphur and phosphorus, 
these elements are largely oxidized to sulphuric and phosphoric 
acids. The sulphur of one pound of protein having the com- 
position of serum albumin, for example, if fully oxidized, would 
yield the equivalent of nearly one ounce by weight of con- 
centrated sulphuric acid. High protein rations, therefore, 
tend to bring about a loss of bases from the body. 

b. Neutralization of acids. — In all these various ways there 
is a constant tendency to disturb the neutrality of the body 
fluids and towards the establishment of an acidosis, to prevent 
which the acids must be neutralized. The significance of 
this was first shown by the experiments of Lunin already re- 
ferred to (421), which showed that the life of animals fed on 
ash-free feed could be considerably prolonged by the addition 
of sodium carbonate to neutralize the acids produced in the 
body. Normally, this neutralization is accomplished in two 
general ways. 

First, an excess of acid may be combined with the ammonia 
which is produced from the amino acids in the katabolism of 
protein (233) and is subsequently converted into urea in the 
liver. A part of this ammonia, however, may be diverted 
from this course and utilized to neutralize acids, the resulting 
ammonium salts being excreted in the urine in place of a cor- 
responding amount of urea. The ammonia arising from the 
putrefactions in the lower intestines (140) may serve the same 
purpose. A small quantity of ammonium salts, arising from the 
neutralization of the acids produced especially in the protein 
katabolism, is normally found in the urine, while the feeding 
of inorganic acids or their injection into the blood stream, or a 
pathological acidosis, may greatly increase their amount. ] 

On the basis of early experiments upon rabbits it has been taught 
that the ability to neutralize acids by means of ammonia is peculiar 
to carnivora and omnivora and is present to a very limited extent in 



338 NUTRITION OF FARM ANIMALS 

herbivora. It seems a priori unlikely that such a difference in the 
metabolic processes should exist, and later investigations have shown 
that there is no such fundamental distinction between the various 
species. It should be remembered, however, that the protein metab- 
olism of herbivorous animals is often on a relatively low plane, and 
that consequently relatively less ammonia may be available than in 
the case of carnivorous animals. 

Another phase of the matter, which has received little considera- 
tion, is the possibility that the long-continued presence of ammonium 
salts in the body may have an injurious effect. The possibility of 
injury through acid rations in this way could hardly be determined 
except by means of experiments, covering, if possible, the whole life 
cycle of the animal. 

Second, an excess of acid may be disposed of by combination 
with the fixed bases present in the body. These are, in the 
first instance, those contained in the carbonates and phosphates 
of the blood and other fluids. Henderson, as already noted, 
has shown that these salts are present in the blood serum in 
such proportions that relatively large amounts of acids may be 
disposed of in this way without materially altering the reaction 
of the blood. 

c. Excretion of acids. — The neutralization of acids produced 
in the body does not, however, necessarily involve the excretion 
of an equivalent amount of base. It is a familiar fact that the 
urine may possess a considerable degree of acidity. The work 
of Henderson shows that the kidneys are able to separate more 
or less of the phosphoric acid from the bases of the blood, ex- 
creting it as acid phosphates in the urine and retaining a cor- 
responding amount of bases in the blood. 

428. The skeleton as a reserve of ash ingredients. — The 
store of bases in the body fluids, however, is limited. The larger 
part of the ash of the body is contained in the skeleton, which 
constitutes a relatively large reserve of basic phosphates and 
carbonates which may be drawn upon to supplement the supply 
in the blood. This fact has an important bearing on the ques- 
tion of the necessary ash supply in the feed, while it must likewise 
be taken into account in experimental work. Long-continued 
maintenance on abnormal feeds or under conditions favoring 
acid production in the body may result in extracting from the 
body comparatively large amounts of mineral matter even to 



MAINTENANCE — REQUIREMENTS OF MATTER 339 

the extent, apparently, of bringing about pathological condi- 
tions, while on the other hand, normal feeding and conditions 
may enable such losses, if not too extensive, to be made good. 
The point which is of special importance is that these fluctua- 
tions of the ash content of the skeleton affect the ash as a whole. 
It was found by Aron that the composition of the bone ash as 
given in Chapter II (81) remains practically constant even when 
the skeleton has been greatly impoverished in total ash. In 
particular this has been shown to be true not only of the calcium 
and phosphoric acid of the bones but also of the minor in- 
gredients such as carbonic acid, magnesium and even sodium. 
A draft upon the skeleton for sodium, for example, could be 
met only by the mobilization of an amount of total bone ash 
containing the requisite quantity of sodium, and this would re- 
sult in throwing into the circulation relatively large amounts 
of calcium and phosphoric acid for which there may be no re- 
quirement, thus raising the percentage of these ingredients 
above the normal limit and leading to their excretion. 



Maintenance of ash balance 

429. Relation to feed. — The foregoing paragraphs clearly 
indicate that the ash requirements for maintenance depend 
chiefly on the amounts of the various ash ingredients which, 
for one reason or another, are thrown into the circulation 
in excess of the body's needs and are therefore removed 
by the excretory organs, and furthermore, that the nature 
of the feed consumed, particularly the relative proportions 
of its ash elements, is an important factor in determining these 
losses. 

430. Deficiencies in ash ingredients. — Some feeding stuffs 
contain relatively little total ash and are especially deficient 
in particular elements. The most striking and familiar example 
of this is maize. According to Henry and Morrison * average 
maize contains about 1.8 per cent of total ash, while its lime con- 
tent is only 0.02 per cent and that of soda only 0.04 per cent. 
Some by-product feeds are similarly poor in particular ingre- 
dients. Obviously such feeds are not by themselves well adapted 

1 Feeds and Feeding, 15th Ed., p. 672. 



34-0 NUTRITION OF FARM ANIMALS 

for growing or milking animals, in which a storage of ash in the 
product occurs. For the simple maintenance of mature an- 
imals, however, which is the topic under discussion, the question 
whether the small amount of lime present, for example, is ad- 
equate depends upon the rate at which lime is being lost from 
the body. If this loss could be reduced to zero, a feeding stuff 
containing no lime whatever would seem to be adequate for 
maintenance so far as that substance is concerned. In general, 
whether a feeding stuff or ration is to be regarded as containing 
an insufficient amount of some ash element for maintenance de- 
pends largely on how it affects those body functions which de- 
termine the rate of excretion of that element. 

431. Acid and basic ash. — It is usually considered that the 
most important relation of feed in the respect just mentioned 
is that which it bears to the maintenance of neutrality in the 
body fluids. Feeding stuffs or rations containing in assimilable 
form much sulphur or phosphorus, for example, tend to cause 
the production in the body of corresponding amounts of sul- 
phuric and phosphoric acids which must be neutralized. On 
the other hand, feeding stuffs containing large proportions of 
the bases tend to have the opposite effect. The relation of acid 
to basic elements has, therefore, an important bearing upon the 
suitability of a feeding stuff for ash maintenance. 1 

Feeding stuffs differ widely in this respect. In general it 
may be said that the concentrates contain relatively much 
phosphorus and sulphur, little calcium and only moderate 
amounts of potassium and sodium, while the roughages, es- 
pecially those of better quality, are rich in calcium and alkalies 
and low in sulphur and phosphorus. A definite measure of 
these differences as related to the maintenance of neutrality in 
the body is obtained by converting the percentages of the 
several ash ingredients into chemical equivalents. 

Alfalfa hay, for example, according to Henry and Morrison, 2 
contains in one kilogram the amounts of ash ingredients shown 
in the first column of the following statement. Dividing 

1 Evidently the sulphur and phosphorus present in organic combination must be 
included in such comparisons as well as the elements present in the form of electro- 
lytes. In the older ash analyses the sulphuric acid represents only that part of the 
sulphur remaining after the material has been ashed, which, as is now known, is but 
a small part of the total sulphur. 

2 Feeds and Feeding, 15th Ed., p. 672. 



MAINTENANCE — REQUIREMENTS OF MATTER 341 

the amount of each by its equivalent weight gives the gram 
equivalents shown in the last two columns, showing that a 
kilogram of this feed contains 1.300 gram equivalents of excess 
base. 





Ash Ingre- 
dients 
per Kg. 


Equivalent 
Weights 


Gram Equivalents 




Acid 


Base 


K 2 

Na 2 .... 

CaO 

MgO .... 
Fe 2 3 .... 
S0 3 

P206 1 . . . . 

CI 


Grms. 

22.3 

5-6 

19-5 

5-9 

i-7 

7.8 

5-4 
4-7 


94-3 

2 
62.1 

2 
56.1 

2 
40.36 

2 
159.8 

6 
80.06 

2 
142.0 

2 
35-45 


O.195 
O.076 

0-I33 
0.404 


Q-473 
0.180 
0.695 
0.292 
0.064 




1.704 



The results of a considerable number of computations of this 
sort by Forbes 2 are contained in Table X of the Appendix, the 
equivalents of bases and acids being expressed in cubic centi- 
meters of normal solution. The table shows clearly that some 
feeding stuffs, like the hays, for example, contain a considerable 
excess of basic ingredients, while others have an excess of acid- 
forming elements. The ratio of phosphorus to calcium, too, 
which is a special case of the ratio of acids to bases, shows 
considerable variations. 

432. Significance of acidity in ash. — Much stress had been 
laid on this distinction between feeding stuffs with acid or 

1 Phosphoric acid is regarded as neutralized when two of its hydrogen atoms are 
replaced by basic elements. 

2 Ohio Expt. Sta., Bui. 255. 



342 NUTRITION OF FARM ANIMALS 

alkaline ash in discussions of both human nutrition and that 
of domestic animals. Doubtless the point is an important one 
but the assumption that all excess of acid over basic elements 
in the diet should be avoided seems hardly warranted, especially 
as regards maintenance. The fact that the body is to a certain 
extent provided with a means of defense against excessive acids 
through its ability to neutralize them by means of ammonia 
and through the power of the kidneys to separate acids and 
bases is sufficient to show that an excess of acid-forming ele- 
ments in the feed is not necessarily injurious. It is only when 
the excess is so large as to exceed the capacity of these regulative 
arrangements and when it therefore begins to draw on the 
fixed bases of .the body, or possibly when it causes the produc- 
tion of large quantities of ammonia, that it becomes a source of 
danger. 

433. Alkali ratio of ash. — As indicated in previous para- 
graphs, the ratio of potassium to sodium in a feeding stuff may 
have an important bearing on the losses of ash from the body. 
It was there stated that while a surplus of potassium salts re- 
sorbed into the blood is promptly disposed of by excretion 
through the kidneys, it may carry along with it more or less 
sodium, so that a ration relatively rich in the former may tend 
to impoverish the body in the latter. Such a loss of sodium 
from the body, it would appear, might have serious indirect 
effects if continued long enough to cause a draft on the stock of 
sodium in the skeleton. Such a draft, as already said (428), 
involves the solution of a corresponding amount of the total 
ash of the skeleton, so that the bones would be impoverished 
in other ingredients, especially calcium and phosphoric acid, as 
well as sodium. In fact it has been found that fodders that 
cause malnutrition of the bones resulting in the disease known 
as rickets (Rachitis) usually show a misproportion of potassium 
to sodium. Zuntz x cites the following comparisons of the ash 
of normal hay with that of hays causing the disease. Along 
with a somewhat greater ratio of phosphoric acid to calcium, 
the injurious hays show a very striking difference in the 
alkali ratio, as appears from the following table to which 
the corresponding figures for cow's milk have been added for 
comparison : — 

1 Jahrb. Deut. Landw. Gesell., 1912, p. 577. 



MAINTENANCE — REQUIREMENTS OF MATTER 343 

Table 63 . — Alkali Ratio of Ash 



Normal Brandenburg hay . . 
Very injurious Brandenburg hay 
Less injurious Brandenburg hay 

Normal Schwarzwald hay . . 
Injurious Schwarzwald hay 

Cow's milk 



K20 


Na 2 


% 


% 


20.00 


5-43 


37-65 


1.74 


33-54 


2.50 


20.88 


4.40 


37-4Q 


0.21 


34 


8 



Ratio 

Na20 to 

K2O 



1 : 

3-68 
21.64 
13.42 

4-75 
178.10 

4-25 



434. Balancing of ash ingredients in the ration. — While 
the animal body has a considerable degree of adaptability to 
variations in the ash supply, and while, during short periods, 
relatively large errors in this respect may be compensated for 
out of the comparatively large stock of ash in the body, never- 
theless, it is clear from previous paragraphs that in the long 
run a reasonably close balance of the ash ingredients in the 
ration is necessary, and tables like that of the Appendix have 
been computed as guides for this purpose. That they convey 
useful information cannot be denied, but any attempt to base 
actual estimates regarding ash maintenance or the ash balance 
on such data overlooks some important considerations. 

Ash not entirely digestible. — It must be remembered that not 
all of the ash ingredients of the feed can be assumed to be di- 
gested and resorbed-. It is true that much of the ash found in 
the feces has really been digested and excreted again in the 
lower intestines but this is by no means true of the entire quan- 
tity. In the case of herbivora, especially, a considerable share 
of the dry matter of the feed escapes digestion and it can hardly 
be daubted that it carries with it into the feces more or less of 
its ash elements. This is particularly true of the sulphur and 
phosphorus of the proteins and the nucleoproteins. So far as 
these escape digestion, they carry their organic sulphur and 
phosphorus with them into the feces without giving it oppor- 
tunity to contribute to acid production in the body. How far 
the same thing is true of the other ash elements it is impossible 



344 NUTRITION OF FARM ANIMALS 

to say, since there is at present no way to determine how much 
of any particular ash ingredient found in the feces consists of 
undigested material and how much is to be regarded as an ex- 
cretory product. This being the case, a table like that of the 
Appendix can give only a general and approximate idea of the 
total quantity of ash or of the balance of its basic and acid 
elements or of the alkalies in the materials actually resorbed 
and entering into the metabolism. 

Influence of supply on excretion. — Moreover, it is necessary 
to take into consideration the influence discussed in previous 
paragraphs (429-433) of the nature and proportions of the ash 
ingredients actually resorbed upon their excretion. For ex- 
ample, potassium may lead to a loss of sodium and this in turn 
to losses of calcium and phosphoric acid, thus possibly affecting 
to a considerable extent the ratio of acid to basic elements in 
the excreta. Adding to this the facts that more or less of the 
acids produced in the body may be neutralized by ammonia 
instead of by fixed bases (427 b), and that the kidneys have the 
power, in some species at least, to separate acids from bases 
(427 c), leading especially to excretion of acid phosphates, it 
is evident that the data of the table may fall considerably short 
of representing the actual value of the feed as regards main- 
tenance of the ash balance. 

435. The ash balance. — These considerations render it evi- 
dent that the value of conclusions as to the balance of income 
and outgo of ash elements drawn from the composition of the 
feeding stuffs concerned must be more or less problematical, 
particularly as regards farm animals. Such conclusions are 
more or less probable deductions from the facts outlined in 
previous paragraphs regarding the functions of ash in the body 
and need to be checked by direct experiments. The actual 
effect of a feeding stuff or ration on the ash maintenance of 
herbivora can be determined with certainty only by means of 
direct comparisons of the income and outgo of all the ash ele- 
ments, i.e. j by determinations of the amounts contained in feed, 
feces and urine (metabolism experiments) or by comparative 
analyses of carefully selected test and control animals (com- 
parative slaughter tests). 

Data of this sort for mature animals are very scanty but 
some tentative conclusions may be drawn from experiments by 



MAINTENANCE — REQUIREMENTS OF MATTER 345 

Diakow * and Cochrane, 2 each on a single steer. Diakow's ex- 
periments include four periods on mixed rations containing 
much hay. In Cochrane's experiments alfalfa hay constituted 
the sole feed, supermaintenance, maintenance and submain- 
tenance rations being consumed. Accordingly, the total ration 
contained in every instance a considerable excess of bases. 
Under those conditions, not only the feces but likewise the 
urine showed an excess of bases over acids, i.e., the animal 
was engaged in getting rid of excess bases. The net residue 
which was retained in the body consisted of basic material of 
rather constant composition even in the case of Diakow's nearly 
mature animal. 

So far as they go, then, these experiments confirm the con- 
clusion that with rations containing a large proportion of 
roughage, there is no reason to fear losses either specifically of 
fixed bases or in general of total ash. Such would almost always 
be the case with the ordinary maintenance rations of cattle, 
sheep and horses. Swine, on the other hand, if maintained 
entirely on grain, might very well receive rations not well 
balanced as regards ash, and experiments and observations 
which are discussed in Chapter XI (492-496) seem to indicate 
that even for maintenance the ordinary grain ration, especially 
if it consists largely of maize, should have its ash composition 
corrected. The effect of an acid ash in the mixed rations of 
herbivora, and the extent to which such acidity can be taken 
care of in the body without drawing on its reserves of ash, has 
still to be investigated. In view of the large amounts of surplus 
bases excreted under the conditions of Diakow's and Cochrane's 
experiments, it would seem likely that even a considerable 
excess of acid elements might be neutralized without drawing 
on the stock of fixed bases in the body. 

In Diakow's experiments, the minimum quantities of 0.115 
lb. calcium and 0.045 lb. phosphorus in the feed per 1000 pounds 
live weight sufficed to support not inconsiderable gains by the 
body. In Cochrane's experiments, a minimum of 0.147 lb. cal- 
cium per 1000 pounds also resulted in a gain, while 0.039 lb. 
phosphorus was just sufficient for maintenance. In Henneberg's 
investigations 3 upon the maintenance of cattle, however, dis- 

1 Landw. Jahrb., 44 (1913), 833. 2 Penna. Inst, of An. Nutr., unpublished results. 
1 Beitrage, etc., Heft, 1 (i860), p. 113. 



346 NUTRITION OF FARM ANIMALS 

tinctly smaller amounts, viz., 0.090 lb. of calcium and 0.021 lb. 
of phosphorus proved adequate for maintenance. Weiske x found 
that a mature sheep gained small amounts of ash ingredients 
on a ration of meadow hay containing, per 1000 pounds live 
weight, 0.179 lb. calcium and 0.045 lb- phosphorus. 

436. Correction of ash deficiencies. — As regards main- 
tenance, it seems clear that the ash requirement is a qualitative 
rather than a quantitative one; i.e., that it is the proportions 
far more than the total amounts of ash ingredients that are 
important. If, then, there is reason to fear that the ash supply 
in the ration is inadequate for maintenance, any measures 
taken to remedy this must be directed chiefly toward the cor- 
rection of the misproportion between different ingredients and 
only secondarily to an increase of their total quantity. 

One method of effecting such a correction is by the direct 
addition of mineral matter. In attempting to correct de- 
ficiencies in this way, however, the simple addition of more ash 
material to the ration may not be effective. It is necessary 
also to take into account the nature of the defects to be made 
good. Maize, for example, has already been instanced (430) 
as a feeding stuff peculiarly low in ash, the exclusive use of 
which, even for maintenance, might readily lead to a loss of 
ash from the body. Maize is especially deficient in calcium and 
its exclusive use would be liable to cause a loss of this element. 
The attempt to supply additional calcium, however, by the 
addition of such materials as calcium phosphate or sulphate 
would not help the situation materially because the ash would 
still remain acid and thus capable of causing a loss of fixed 
bases irrespective of the additional amount of calcium present. 
On the other hand the addition of calcium in the form of car- 
bonate, by the use of precipitated chalk or wood ashes, not 
only supplies additional calcium but remedies the acid con- 
dition which leads to a loss of that element, as has been well 
demonstrated in the numerous experiments on growing swine 
referred to in Chapter XI (496). The correction of the ash 
composition of hays causing malnutrition of the bones, like 
those instanced by Zuntz (433), presents quite different re- 
quirements. The very injurious Brandenburg hay, e.g., con- 
tained the following percentages of ash ingredients : — 

1 Landw. Jahrb., 9 (1880), 290. 



M 



MAINTENANCE — REQUIREMENTS OF MATTER 347 

Table 64. — Ash of Hay Causing Rickets 



CaO 

MgO 

K 2 

Na 2 

SO3 (Estimated from protein) 

P 2 5 

CI 



Per Cent 



0.693 
0.308 
1.762 
0.082 
2.650 
0.380 
0.722 



Gram Equivalents 



Acid 



0.0668 

0-0535 
0.2037 



0.3240 



Base 



0.2470 
O.1526 

0-3737 
O.0264 



0.7997 



Such a hay is relatively deficient in calcium and phosphorus 
and would presumably be improved by the addition of calcium 
phosphate, while the addition of calcium carbonate would 
probably be unnecessary, since the hay contains an excess of 
basic over acid ingredients. In addition, however, to its de- 
ficiency in calcium and phosphorus, it shows a misproportion 
of potassium to sodium, which, as already explained, would 
tend to increase the excretion of calcium phosphate unless 
sodium salts, particularly the chlorid, were added. 

In the mixed rations of herbivora, however, direct addition 
of mineral matter is seldom likely to be necessary unless rough- 
age of abnormal quality is employed. Usually the surplus of 
bases in forage crops will more than balance the surplus of 
acid elements in the concentrates used, while the common salt 
ordinarily given as a condiment will more than balance any 
probable excess of potassium in the rations. Unusual rations, 
such perhaps as very heavy grain rations, those containing an 
unusual proportion of protein, or those made up of unusual 
feeds may form an exception to this general rule and require 
special consideration. In the case of swine, such a balancing 
of one feeding stuff against another as regards ash ingredients 
is less practicable, and the securing of a proper balance needs 
more attention. Until, however, more determinations of the 
actual ash balance of different species on different classes of 
rations are made (435) it is hardly possible to state with any 



348 NUTRITION OF FARM ANIMALS 

definiteness what proportions of the different ash elements are 
required in maintenance rations and the whole subject offers 
a wide field for investigation. 

§ 3. Accessory Substances 

Leaving out of account the fact that the proteins are a minor 
source of energy and considering only the requirements for 
matter, the proteins and ash elements of the feed are required 
substantially for maintenance, i.e., to make good losses of the 
structural elements of the body, especially if the ash content 
of the body fluids be included under this designation. Recent 
investigations, however, have revealed the presence in the feed 
of minute amounts of substances which appear to bear quite 
a different relation to nutrition and which may be called for 
convenience, accessory substances. 

437. Vitamins. — Attention was first called to these acces- 
sory substances through investigations into the cause of the 
tropical disease known as beri beri. It has been shown that 
this is a nutritional disease, resulting from a preponderance in 
the diet of so-called " polished " rice, i.e., rice from which the 
seed coats have been removed. It is a tropical disease only in 
the sense that many inhabitants of the tropics subsist largely 
on rice. It has been shown that it can be produced in Europe 
by the excessive use of this grain. 

Substantially the same disease (polyneuritis) may be induced 
in animals, especially in fowls, by an exclusive diet of polished 
rice and it is to experiments on these animals that most of our 
imperfect knowledge of the subject is due. 

It has been shown that in man beri beri may be prevented 
by the use of a rational dietary, and especially by the substitu- 
tion of rough rice or of other grains for polished rice. Experi- 
ments on animals have shown that a subject fed on polished 
rice until nearly at the point of death may be restored to normal 
condition in a short time by the administration of small amounts 
of an aqueous extract of rice bran, the improvement being so 
rapid as to appear almost miraculous. The generally accepted 
explanation is that the bran contains a small amount of a water- 
soluble substance or substances necessary for the normal func- 
tioning of the body, the lack of which in polished rice gives 



MAINTENANCE — REQUIREMENTS OF MATTER 349 

rise to the disease. Aqueous extracts of other substances, 
notably yeast, are capable of producing the same curative effects. 
The substances themselves have not yet been isolated but 
Funk, 1 who has been prominent in this line of investigation, 
has given them the general name of vitamins. It is thought 
that other nutritional diseases, such as scurvy and pellagra, 
as well as the cotton-seed poisoning of swine, are likewise due 
to the use of diets deficient in these vitamins. 

438. Growth substances. — Very interesting facts of a some- 
what similar character have been observed regarding growth, 
notably by Hart and McCollum, and by Osborne and Mendel. It 
seems to have been demonstrated that there are associated with 
certain fats, such as butter fat, the fat of egg yolks, cod liver 
oil, etc., substances whose absence from a ration otherwise 
adequate renders it incapable of permanently supporting 
growth. That this substance (or substances) differs from the 
vitamins of Funk seems apparent from the fact that norma] 
maintenance may apparently be secured on rations from which 
it is absent. 

The very interesting results obtained by Hart, McCollum, 
Steenbock and Humphrey 2 with cows fed rations properly 
balanced according to the ordinary criteria but made up from 
the products of single plants (wheat, oats, maize) suggest that 
substances similar to the vitamins or the growth substances 
may play an important part in the nutrition of farm animals. 
These rations when continued for two or three years mani- 
fested specific differences in nutritive effect as regards growth 
and reproduction, although all of them seemed to be fairly ade- 
quate for the maintenance of live weight. 

Most investigations upon these accessory substances, however, 
have been directed to their relation to growth and further 
discussion of their functions in nutrition may therefore be 
deferred until that subject is considered. 

1 Ergeb. Physiol., 13 (1913), 125. 

2 Wis. Expt. Sta., Research Bui., No. 17 (191 1). 



CHAPTER X 

THE FATTENING OF MATURE ANIMALS 

439. Disposal of surplus feed. — When an animal consumes 
feed in excess of that required simply for maintenance, a pro- 
duction of some sort results. The surplus feed may be trans- 
formed into material products as flesh, fat, milk, etc., which 
are stored up in the body or secreted, or it may be katabolized 
and its energy expended in the performance of work. 

One of the simplest and most familiar examples of such pro- 
duction is afforded by the fattening of mature animals. Such 
fattening, it is true, is not of great economic importance, since 
the larger share of the world's meat supply is derived from 
animals which have not yet reached full maturity. Fattening, 
however, as well as growth, forms an essential part of the pro- 
duction of at least the better grades of meat, and while it is 
practiced largely on immature animals its feed requirements 
can be studied to better advantage in the mature animal. The 
purpose of the present Chapter is to consider the general nature 
of the fattening process and the demands which it makes upon 
the feed supply, leaving its economic aspects for discussion in 
connection with meat production. 

440. Fattening requirements. — Just as the quantities of 
matter and energy required for maintenance depend, in the 
first instance, upon the amounts lost from the body during 
fasting, so the quantities which must be supplied in excess of 
maintenance to support the fattening process will depend 
primarily on the amount and composition of the gain made. 
The obvious first step in considering the feed requirements of 
the fattening animal, therefore, is a study of the composition of 
the increase. 

§ i. Composition of the Increase in Fattening 

441. Increase chiefly fat. — The discussions in previous 
chapters have rendered it evident that the chief function of 

350 



THE FATTENING OF MATURE ANIMALS 351 

the fat contained in the animal body is that of a reserve of 
energy for the vital activities, which may be drawn upon when 
the feed supply is insufficient and replaced when feed is abun- 
dant, while the protein of the mature animal is subject to much 
smaller fluctuations. It would be expected, therefore, that the 
gain made by a mature animal on a liberal ration would consist 
largely of fat. That such is indeed the case has been shown 
in two ways, viz., by means of comparative analyses of the car- 
casses of lean and fattened animals, i.e., comparative slaughter 
tests (284), and by means of balance experiments (285) from 
which the composition of the organic matter gained may be 
computed. 

442. Comparative slaughter tests. — The classic example of 
this method is Lawes and Gilbert's well-known investigation l 
into the composition of animals slaughtered for human food, 
the results of which are recorded in Chapter II (97). 

The two pigs analyzed were from the same litter, and were believed 
to be very closely comparable at the beginning, so that it was possible 
to compute directly the composition of the increase during fattening. 
The other animals analyzed were not regarded as comparable. In 
order to estimate the composition of the increase in cattle and sheep, 
Lawes and Gilbert compute the weights of protein, fat, ash and total 
dry matter contained in the bodies of a large number of animals 
before and after fattening, using in the former case the analytical 
results obtained on the half-fat ox and the store sheep and in the 
latter those on the fat ox and fat, sheep. The differences, of course, 
show the gain of each ingredient. In the case of sheep and swine, 
they utilize the results of their own fattening experiments. In the 
case of cattle, the computations are based upon the results of experi- 
ments by others. The oxen whose composition was compared were 
mature animals. The sheep, on the other hand, were yearlings. 
Neither the age nor the weight of the pigs is stated, but their pig 
feeding experiments in general were made with animals ranging from 
somewhat over 100 lb. to 160 lb. in weight. The results as to this 
species, therefore, presumably relate to only partially mature animals. 

In 1876-1877, Henneberg, Kern and Wattenberg 2 investigated 
the composition of the increase in weight of mature sheep in 
fattening. Their analyses were of the carcasses only but the 

1 Phil. Trans., II, 1859, p. 493. 2 Jour. Landw., 26 (1878), 545. 



352 



NUTRITION OF FARM ANIMALS 



weights of the offal parts were recorded, so that it is possible 
to compute approximately the weight of the fat-free body, 
exclusive of the contents of the digestive tract and of the wool. 
Similar comparisons based on 75 and 82 day fattening periods 
with swine were reported by Soxhlet l in 1881 and the results 
of short fattening experiments (16 to 37 days) on geese by B. 
Schulze 2 in 1882 and by Chaniewski 3 in 1884, the primary 
object of each case being a study of the sources of animal fat. 
Friske 4 in 1909 and Pfeiffer and Friske 5 in 191 1, in a study of the 
gain of protein by mature animals during a fattening period of 
about 100 days, likewise reported a number of partial analyses 
of mature sheep similar to those made by Henneberg, Kern 
and Wattenberg. 

Table 65. — Composition of Increase in Live Weight in Fattening 



Cattle 
Lawes and Gilbert . . 

Sheep 
Lawes and Gilbert . . 
Henneberg, Kern and 
Wattenberg . . . 

Fat 

Very fat 

Last stage of fattening 

Friske 

Pfeiffer and Friske . . 

Swine 
Lawes and Gilbert (Aver- 
age) ...... 

Soxhlet — Swine No. 2 . 
Swine No. 3 . 
Geese 

Schulze 

Chaniewski 



Average 
Age of 
Animal 



4 years 
1 i years 



2 j years 
2! years 
2 I years 
4 years 
32 years 



16^ mos. 
i6| mos. 

9 mos. 



Composition of Increase 



Water 

% 



24.64 
20.13 



Ash 
% 



1.47 
2-34 



25.80 
20.30 

6-45 
12.03 

64.33 



22.00 
58.96 
35-99 

37.06 
24.15 



0.06 

3-i7 
3.62 

1. 21 

i-37 



Protein 

% 



7.69 
7-13 



6.64 

5-23 
1.68 

15-07 
7.11 



6.44 

13.42 

6.80 

3-34 
3.02 



Fat 

% 



66.20 
70.40 



67.56 

74-47 
91.87 
72.90 
28.56 



71.50 
24-45 
53-59 

58.39 
61.46 



Energy 
Content 

of 
Increase, 
Calories 

per Lb. 



3051 
3218 



3083 

3344 
4002 

3531 
1415 



3247 
1401 

2485 

2602 
2726 



1 Centbl. Agr. Chem., 10 (1881), 674. 3 Ztschr. Biol., 20 (1884), 179. 

2 Landw. Jahrb., 11 (1882), 57. * Landw. Vers. Stat., 71 (1909), 441. 

6 Ibid., 74 (1911), 409. 



THE FATTENING OF MATURE ANIMALS 



353 



The results of these comparative slaughter tests, so far as 
they relate to the composition of the increase, are summarized 
in Table 65, which includes also the computed energy content 
of the increase. 

443. Respiration experiments. — Respiration experiments on 
mature animals have fully confirmed the results of slaughter 
tests as 'regards the proportion of protein to fat in the increase, 
as appears from the summary of Table 66. 

By far the most extensive respiration experiments are those made 
at the Moeckern Experiment Station x by G. Kiihn and by Kellner 
on mature fattening cattle. Of the 60 reported experiments in 
which there was a gain of both protein and fat, only 3 show less 
than 70 per cent of fat in the total organic matter gained and only 
3, a percentage above 95. Rejecting these 6 and grouping the re- 
mainder according to the percentage of fat gives the results shown 
in the first five lines of the table. To these are added the results of 
earlier experiments by Henneberg, Fleischer and Miiller 2 on sheep 
and by Meissl 3 on swine. The gains of ash and of water were not 
determined in these experiments. 

Table 66. — Proportions of Protein and Fat in Fattening Increase 



Kellner — Experiments on cattle 

Group I 

Group II 

Group III 

Group IV 

Group V 

Henneberg, Fleischer and Miiller — Ex- 
periments on sheep 

Meissl, Strohmer and Lorenz — Experi- 
ments on swine 

Animal No. 1 

Animal No. 2 

Animal No. 3 

Animal No. 4 



Range of 

Percentage 

of Fat in 

Organic 

Matter 

Gained 



% 
70-74.99 

75-79-99 
80-84.99 
85-89.99 
90-94.99 



Average Composition 

of Organic Matter 

of Gain 



Total 
Protein 



% 

26.25 

23-30 
17.17 

12-55 
8.06 

4.26 



9-75 
10.67 
16.39 
15.16 



Fat 



% 

73-75 
76.70 
82.83 

87-45 
91.94 

9 r -74 



90.25 

89-33 
83.61 
84.84 



1 Landw. Vers. Stat., 44 (1894), 370; 53 (1900), 1. 

2 Jahresber, Agr. Chem., 16-17 (1876), II, 145. 3 Ztschr. Biol., 22 (1886), 63. 

2 A 



354 



NUTRITION OF FARM ANIMALS 



Both the respiration experiments and the comparative 
slaughter tests demonstrate that the fattening of a mature 
animal is, as its name implies, largely a production of fat, 
which is deposited chiefly in the sub-cutaneous and internal 
adipose tissue and to a limited extent also in the muscles. A 
few of the comparative slaughter tests show a large storage of 
water but the organic matter gained in every case was chiefly 
fat. On the average of all the foregoing experiments by both 
methods, the composition of the organic matter stored up in the 
body of the fattening animal was as follows : — 

Table 67. — Average Composition of Organic Matter Gained in 

Fattening 



Fat . 
Protein 



Mean 


Maximum 


87.16% 

12.84% 

100.00% 


95-74% 
35-43% 



Minimum 



64-57% 
4-26% 



444. The gain of protein. — The foregoing data also show, 
however, that while the gain of dry matter in fattening consists 
chiefly of fat there is also a gain of more or less protein and of 
small amounts of mineral matter. 

The actual gain of protein in some cases was not inconsiderable. 
This appears from Table 68, which includes both slaughter tests and 
metabolism experiments, most of which are identical with those from 
which the composition of the increase has been calculated. 

It is probably safe to assume that in most of these experi- 
ments the feed contained a considerable surplus of protein 
over that necessary for maintenance. Such a surplus of pro- 
tein, as was shown in Chapter IX (406), has a tendency to pro- 
duce a somewhat limited storage of protein, which probably con- 
sists in an increase of the contents of the cells or of the protein 
held in solution in the body fluids rather than in an increase of the, 
structural elements of the body. The observed gain, therefore, 
may represent in part an actual increase in the cell protoplasm 
or in the soluble protein of the body, while in addition, a rela- 
tively small amount is accounted for by the growth of hoof, 
horn, epidermis, etc., of the cattle and swine. Moreover, 



THE FATTENING OF MATURE ANIMALS 



355 



while the laying on of fat is accomplished largely by an increase 
in the fat-content of existing cells there appears to be also an 
increase in the number of cells in the adipose tissue, and the 
latter process may be assumed to require a supply of protein. 
The protein contained in one pound of subcutaneous adipose 
tissue of average composition would be equivalent to the 
storage of about 0.045 lb. of protein. Obviously, however, the 
growth of epidermal and adipose tissue can but partially ac- 
count for the observed gain of protein in many of these instances 
and apparently a distinct increase of the nitrogenous tissue in 
fattening must be admitted, averaging, in these experiments, 
about 0.2 pound per day and 1000 pounds live weight or about 
5.5 per cent of the total increase in live weight. 

Table 68. — Gain of Protein by Mature Animals 



Cattle 

Kiihn and Kellner 

Sheep l 
Henneberg, Fleischer and Mul- 

ler 

Weiske 

Henneberg, Kern and Watten- 

berg 

Henneberg and Pfeiffer . 

Pfeiffer and Kalb 

Friske 



Pfeiffer and Friske . 
Swine 



Soxhlet 



Meissl 



Geese 



Schulze 



Character of 
Experiment 



Metabolism 

Metabolism 
Metabolism 

Slaughter 
Metabolism 
Metabolism 
Metabolism 2 
Slaughter 

Metabolism 
Slaughter 

Slaughter 

Metabolism 

Slaughter 



Aver- 
age 
Live 

Weight 



Kgs. 

667 



34-2 
54-8 

48.3 
43-5 
38.5 

35-2 
35-2 

36.7 
36.7 

"7-5 

70.0 

104.0 

125.0 

{ 140.0 

3-9 



Daily Gain of 
Protein 



Per 
Head 



Grams 

82.0 



8.50 
9.24 



36.45 



Per 1000 
Live Wt. 



O.123 



O.248 
O.169 



4-05 


0.084 


10.36 


0.238 


6.55 


0.170 


21.49 


0.611 


8.42 


0.239 


7.67 


0.209 


4-55 


0.124 


51.96 


0.442 


46.92 


0.670 


43-32 


0.416 


32.76 


0.262 


36.48 


0.261 



9.346 



1 The nitrogen of the wool is not included in the gain. 

2 The same animals were used also in the slaughter tests. 



356 



NUTRITION OF FARM ANIMALS 



445. Influence of fattening on the composition of the lean 
meat. — While fattening consists largely in an increase of adi- 
pose tissue in the ordinary sense, it has an important effect 
both upon the composition of lean meat in the commercial 
sense and upon that of the muscle tissue proper (fat-free 
lean meat). 

Percentage of fat. — What is commonly spoken of as lean 
meat is by no means free from fat, since the term includes not 
only muscular fibers themselves with the relatively little fat 




Fig. 37. — The marbling of meat. Porterhouse steak from a prime steer. 
(Illinois Experiment Station.) 



which they contain, but the masses of connective tissue of all 
degrees of magnitude found between the muscle bundles and 
between the separate muscles (86). Fattening, especially in- 
tensive fattening, may cause a marked increase in the storage 
of intramuscular fat in the lean meat, as is evident to the eye 
in the so-called " marbling." 

Such analyses of lean meat as are recorded confirm the evi- 
dence of the eye in this respect. A summary of the results on 
this point has been given by the writer * elsewhere. The fol- 
lowing example taken from that publication may serve to 
illustrate the point in question. 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), p. 33. 



THE FATTENING OF MATURE ANIMALS 357 

Table 69. — Fat in Fresh Lean Meat — Leyder and Pyro 



Neck . . 
Leg . . 
Flank 
Tenderloin 



Lean Cow 


Fat Ox 


% 


% 


1-3 


1.0 


0.9 


4.0 


0.8 


4-3 


2.6 


8.0 



Very Fat 
Cow 

% 



2.8 

5-8 

8.8 

12.9 



Similarly, Braman x found the following percentages of fat 
in lean meat from a medium fat (common) and a well-fattened 
(prime) steer. 

Table 70. — Fat in Fresh Lean Meat — Braman 



Porterhouse 
Round . . 




12.71 
6.66 



A practical difficulty in making such comparisons arises in the 
preparation of the sample. Obviously, the subcutaneous fat sur- 
rounding the meat should be discarded and the same is true of the 
large masses of fat found between the muscles, but just what part of 
the adipose tissue scattered through the meat of a fat animal should 
be regarded as mechanically separable and what part should be re- 
garded as belonging to the meat proper is difficult to decide. Dif- 
ferences in the trimming of the pieces may account for some of the 
irregular results found by recent experimenters. 

Extractives. — It appears to be established that fattening 
increases the nitrogenous extractives of the muscles as well as 
causes a deposition of fat in and about them. For example, 
in Henneberg, Kern and Wattenberg's experiments on sheep, 
included in Table 65, the composition of the meat from the lean 
and from the very fat animal (partially freed from connective 
tissue) computed to the fat-free state, was : — 

l Ibid., Bui. 128 (1908), p. 86. 



358 NUTRITION OF FARM ANIMALS 

Table 71. — Composition of Fat-free Meat of Sheep 



Water 

Insoluble protein . 
Extractives 

Soluble protein . 

Non-protein . . 

Ash 

Total extractives 



Thin Sheep 



79.41 
15.85 



I.29 
2.18 
1.27 



Very Fat Sheep 

% 



i-93 
2.17 

1. 15 



79.02 
15-73 



5-25 
100.00 



It is computed that the actual gains during the fattening of 
the fat animal were as follows : — 

Insoluble protein 38.7 Grms. 

Extractives : 

Protein 82.0 Grms. 

Non-protein 4.2 Grms. 

Ash —9.2 Grms. 

77.0 Grms. 
Total 1 15.7 Grms. 

Somewhat similar results were obtained later by the same 
authors in experiments on fattening lambs. Evidently this 
increase in the soluble nitrogenous compounds of the muscles 
is one of the factors going to make up the observed gain of 
protein by fattening animals. 

446. Object of fattening. — The fattening of animals as a 
commercial process is a practice based on experience, which 
has shown that the tenderness and palatability of the meat are 
materially increased thereby, so that the consumer is willing to 
pay a higher price for it. It is to this improvement in quality 
in the first instance, and only secondarily to the gain in weight, 
that the feeder looks for his profit. 

The facts as to the composition of the increase in fattening 
recorded in the foregoing paragraphs serve to show what are 
the principal factors in this improvement in the quality of the 
meat. They are, first, the deposition of the intermuscular 



THE FATTENING OF MATURE ANIMALS 359 

and intramuscular fat, and, second, an increase in the muscular 
tissues themselves, due in part at least to an increase in the 
soluble protein and in the nitrogenous extractives. The dep- 
osition of fat adds directly to the nutritive value of the meat, 
materially increasing its fuel value. Moreover, its mechanical 
effect in separating the fibers may be presumed to render the 
meat more tender, while the products of its decomposition in 
some forms of cooking (roasting and broiling) probably add to 
the flavor of the meat. The increase of the soluble protein is 
also doubtless one cause of the tenderness of the meat of fat- 
tened animals, while the other nitrogenous matters, though 
of little or no direct nutritive value, are an improvement through 
the added flavor and palatability which they bring about. 

§ 2. Feed Requirements for Fattening 

447. Comparison with maintenance. — In the two preceding 
chapters it appeared that the maintenance requirements are 
determined substantially by the amounts of protein and of 
energy which are katabolized in fasting and which, therefore, 
must be made good from the feed in order to maintain the body. 
By analogy, the amounts of protein and energy stored up in the 
process of fattening may be taken as the measure of the require- 
ments for fattening — i.e., of the amounts which the feed must 
be capable of supplying in an available form. In other words, 
the requirements for fattening are equivalent to the tissue 
produced just as the requirements for maintenance are equiva- 
lent to the tissue whose loss is to be prevented. The 
total feed requirement of a fattening animal, then, is to be 
regarded as made up of the maintenance requirement plus the 
fattening requirement. 

In one important respect, however, the fattening require- 
ment differs from the maintenance requirement. The latter, 
while not invariable, is still more or less constant for the same 
animal. In fattening, on the other hand, there may be a 
varying rate of production up to the limit set by the in- 
dividuality of the animal and its capacity to eat and digest 
food. Accordingly, as slow or rapid fattening is anticipated 
or desired, the daily requirement of the animal may be higher 
or lower. 



3 6 ° 



NUTRITION OF FARM ANIMALS 



Net energy values for fattening 

448. General conception. — Physiologically, the process of 
fattening may be regarded as a storing up by the animal, against 
a possible future scarcity, of feed energy supplied in excess of 
its immediate needs. 

This storage of energy is not accomplished without some loss. 
As in maintenance feeding, so in fattening, a considerable 
portion of the feed energy escapes utilization for one reason or 
another. The conception of the net energy value as express- 
ing that part of the feed energy which remains available after 
these various losses have been deducted, has been considered 
in Chapter VIII. The same conception may be extended to 
fattening rations. Just as the net energy value of a feed for 
maintenance is measured by the loss of body energy which it 
prevents, so its net energy value for fattening is measured by 
the storage of body energy brought about. 

449. Method of determination. — This conception, as well 
as the method of determining the net energy value for fatten- 
ing, may be illustrated by the following respiration experiment 
by Kellner upon a mature ox, in which meadow hay was added 
to a mixed basal ration already sufficient to cause some gain. 
The second column of the table shows the metabolizable energy 
of the two rations, the third column the computed heat pro- 
duction, and the fourth the energy contained in the observed 
gain of protein and fat. 

Table 72. — Determination of Net Energy Value for Fattening 



Basal ration + hay . , 
Basal ration . . . . , 

Difference . . . . , 
Difference per lb. of hay 



Hay 

Added to 
Basal 
Ration 


Metabo- 
lizable 
Energy of 
Ration 


Computed 
Heat 
Pro- 
duced 


Lb. 

7-7 

7-7 


Therms 

23.14 
17.64 

5-5o 
0.714 


Therms 

18.90 
15.62 

3.28 
O.426 



Energy of 
Fat and 
Protein 

Gained by 
Body 



Therms 

4.24 
2.02 

2.22 
0.288 



Each pound of hay added to the basal ration resulted in a 
gain of protein and fat containing 0.288 Therm of energy. 



THE FATTENING OF MATURE ANIMALS 361 

This was its net energy value for fattening. A comparison 
with Table 37 in Chapter VIII (364), showing the results of a 
determination of the net energy value for maintenance, renders 
evident the identity of the method employed in the two cases, 
the only difference being that in one case the comparison be- 
tween the two rations is made below the point of maintenance 
and in the other case above it. It is evident that in fattening, 
as in maintenance feeding, there is a considerable expenditure 
of energy consequent upon the consumption of feed, so that 
only part of the metabolizable energy is actually stored up in 
the gain by the body. In the experiment given as an illus- 
tration, one pound of the hay contained 0.714 Therm of 
metabolizable energy, of which only 0.288 Therm or 40.7 per 
cent was recovered in the gain. 

450. Relative values for maintenance and for fattening. — 
The same causes which were considered in Chapter VIII (367) 
are of course operative to bring about the increased expendi- 
ture of energy on the heavier rations of the fattening animal. 
In addition, it would appear that the chemical changes in- 
volved in the formation of fat from proteins and carbohydrates 
would result in more or less evolution of heat. Whatever 
expenditure of energy may be thus caused is additional to that 
caused directly by feed consumption under maintenance con- 
ditions and must evidently tend to reduce the net energy value 
of the feed by a corresponding amount ; in other words, the net 
energy values of feeding stuffs for fattening would tend to be 
lower than those for maintenance. Such data as are available, 
however, do not appear to indicate that this difference is a 
considerable one in the case of farm animals, and it would appear 
that, in the case of cattle at least and presumably in that of other 
species, the net energy values of feeding stuffs may be regarded 
as being substantially the same for fattening as for maintenance. 1 

Energy requirements for fattening 

451. Energy content of gain. — Since the net energy value 
of a feeding stuff or ration for fattening, as explained in the 
foregoing paragraphs, is that part of its total energy which can 
be stored up by the animal in the increase, it follows that the 

1 Compare Armsby and Fries, Jour. Agri. Research, 3 (19 15), 435. 



362 NUTRITION OF FARM ANIMALS 

ration of such an animal must supply an amount of net energy 
equal to the maintenance requirement plus the quantity of 
energy contained in the gain made. The latter quantity, how- 
ever, may be computed approximately from the data given in 
§ 1 regarding the chemical composition of the increase in live 
weight during fattening. Estimating the energy content of 
protein at 2586 Cals. per pound (5.7 Cals. per gram) and that 
of fat at 4309 Cals. per pound (9.5 Cals. per gram), the energy 
content of one pound of increase was as shown in the last col- 
umn of Table 65 (442). 

Excluding two apparently questionable results, 1 the range 
and average of the remainder are as follows. Although some- 
what variable they indicate that on the average of an entire 
fattening period a pound of increase in live weight in cattle, 
sheep and swine is equivalent to about 3.25 Therms. 

Table 73. — Energy per Pound Increase in Live Weight 

Maximum 4.002 Therms 

Minimum 2.485 Therms 

Average 3-245 Therms 

452. Influence of stage of fattening. — The results just cited 
are in most cases those of an entire fattening period. There 
can be little doubt, however, that the composition of the in- 
crease and its energy content vary materially as the fattening 
advances. 

This appears clearly from Henneberg, Kern and Wattenberg's re- 
sults upon sheep. The "fat" animal had been fed for 10 weeks and 
was regarded as fat according to local standards. The "very fat" 
animal had been fed for 29 weeks, or until no further gain in live 
weight occurred. As the table shows, the total gain by the "very 
fat" animal contained materially lower percentages of water, ash 
and protein and a higher percentage of fat, and had a 10 per cent 
higher energy content than the gain by the "fat " animal, while a com- 
parison between the "fat" and the "very fat" animals shows the 
gain made by the latter during the last 19 weeks of fattening to have 

1 Pfeiffer and Friske's results appear exceptional, since the gain apparently con- 
sisted to an abnormally large extent of water, while the authors themselves point out 
that the gains of dry matter were notably less than should have been produced from 
the feed consumed. It would seem, therefore, that their omission is justified. Soxh- 
let's result upon swine No. 1 has also been omitted for a similar reason. 



THE FATTENING OF MATURE ANIMALS 363 

contained nearly 92 per cent of fat and to have had an energy content 
of 4002 Cals. per pound. The same investigators also obtained en- 
tirely similar results in the fattening experiments on lambs cited in 
Chapter XI (458) although naturally the proportions of wa,ter and 
protein in the increase were greater thap in the case of the mature 
sheep. 

During the earlier stages of fattening, especially with thin 
animals, the storage of fat is accompanied by a considerable 
gain of water and by more or less increase in body protein. As 
the fattening progresses, however, the gain comes to consist 
to an increasing extent of fat accompanied by very little protein 
and a relatively small percentage of water. The energy 
content of a unit of gain in live weight, therefore, in the later 
stages of fattening is materially greater than in the earlier 
stages of the process. Evidently, then, more net energy will 
be required in a fattening ration to produce a pound of increase 
in live weight toward the close of the fattening process than at 
its beginning, a fact which is entirely in harmony with the ex- 
perience of feeders that gains become increasingly expensive as 
the animals become fatter. 

So far as definite conclusions are warranted from the rather 
scanty data available, it would seem that in the earlier stages 
of fattening a ration supplying (in addition to maintenance) 
about 2.5 Therms of net energy would be sufficient to support 
a gain of a pound of live weight, while in the later stages the 
requirement may rise to 4.0 Therms or perhaps even more. 

Protein requirements for fattening 

453. Protein unnecessary for fat production. — It was 

shown in Chapter V (247-249) that body fat, especially in the 
case of farm animals, .is derived chiefly from the non-nitrog- 
enous nutrients of the feed, protein playing but a subordinate 
role in its production, and Kellner has shown (769) that the 
proportion of the energy of protein which can be stored up by 
mature fattening animals is distinctly less than the correspond- 
ing percentage for the non-nitrogenous nutrients. So far as 
simple fat production is concerned, therefore, it would appear 
that a surplus of protein over that required for maintenance 
would be unnecessary and possibly disadvantageous on account 



364 NUTRITION OF FARM ANIMALS 

of its tendency to stimulate the general metabolism of the body 
(365). 

454. Protein in increase. — As appeared in § 1 (444), how- 
ever, the actual increase in mature fattening animals has been 
found to contain a relatively small and rather variable propor- 
tion of protein, due in part to the growth of epidermal tissue, 
in part to an increase in the number of fat cells, and in part 
to an actual storage of protein and nitrogenous extractives 
in the muscular tissue (and in the internal organs?). It is to 
be remarked, however, that in most or all instances the rations 
consumed contained more protein than was necessary for main- 
tenance, with, of course, an abundant supply of non-nitrog- 
enous material, so that the conditions were favorable for such 
a storage of protein as that just mentioned. So far as the writer 
is aware, it has not yet been shown that the mature fattening 
animal actually requires any surplus of protein over the amount 
necessary for maintenance, although it can apparently utilize an 
excess, at least to some extent, to increase the stock of protein 
in its body. 

At most, the requirement of the fattening animal as meas- 
ured by the observed storage of protein is relatively small, one 
pound of increase in live weight containing in round numbers 
from 0.02 lb. to 0.08 lb. of protein. 

455. Utilization of feed protein. — Assuming the observed 
gain of protein by the fattening animal to represent a real re- 
quirement, it is evident that a sufficient fattening ration must 
supply, in addition to the protein necessary for maintenance, 
an additional amount sufficient, after undergoing the various 
processes of digestion and metabolism, to yield the amount of 
body protein contained in the increase of body weight. As 
will appear more particularly in considering the subject of 
growth (470, 471), little is known regarding the amount of feed 
protein required to yield a unit of body protein. Doubtless 
this will differ as between different individual proteins, depend- 
ing, for one thing, upon the proportions of the different amino 
acids which they contain, but adequate quantitative data are 
as yet unavailable. 

456. Protein in fattening rations. — In the absence of definite 
knowledge regarding the availability of the protein of the feed, 
the question of the amount of this nutrient which should be 






THE FATTENING OF MATURE ANIMALS 365 

supplied to fattening animals may be approached much as was 
the question of the amount necessary for maintenance in Chap- 
ter IX, i.e., by inquiring what is the least amount of digestible 
protein which, along with sufficient non-nitrogenous nutrients, 
has sufficed to support a satisfactory rate of fattening. If it 
appears that of two similar animals or lots of animals receiving 
equal amounts of feed, the one consuming the smaller amount 
of protein gave equally satisfactory gains, both as judged by 
the live weight and by the block test, it may be concluded that 
the smaller amount of protein was at least sufficient, although 
it cannot be determined whether it may not have been greater 
than was actually necessary. 

Unquestionably, the protein requirements of mature fatten- 
ing animals have been greatly overestimated in the past. Wolff's 
original feeding standards (791), published in 1864, recommended 
for fattening rations per thousand pounds live weight the follow- 
ing amounts of digestible protein : — 

Cattle 2.5-3.0 lb. 

Sheep 3-Q-3-5 lb. 

Swine . 2.7-5.0 lb. 

Substantially these same figures have been repeated more 
or less uncritically from publication to publication, with a few 
exceptions, even up to the present time. It is clear, however, 
from Wolff's writings that his standards were based upon the 
then prevailing views of Voit and Pettenkofer (248) regarding 
the importance of protein as a source of animal fat rather than 
upon actual experimental results. Subsequent investigations, 
notably the respiration experiments of Kellner upon cattle 
(p. 367), have fully demonstrated that such large amounts of 
protein are neither necessary nor especially advantageous for 
fattening. 

Sheep. — Indeed, Wolff himself has- demonstrated that his protein 
standard for sheep was unnecessarily high. In 1890, he published l 
the results of a comparison made in 188 5- 1886 of maize and beans as 
feed for fattening sheep, using two lots of two mature sheep each. 
After a preliminary feeding, the following results were obtained in 
107 days' feeding : — 

1 Landw. Jahrb., 19 (1890), 823. 



3 66 



NUTRITION OF FARM ANIMALS 



Table 74. — Influence of Protein Supply on Gain by Mature Fat- 
tening Sheep 



Weight at beginning 

Weight at close 

Gain 

Digestible matter eaten per 1000 kilograms 
live weight 
Protein 

Total digestible (fat X 2.4) . . s . . . 



Lot i, Fed 
on Hay 

and Beans 



Kgs. 

99-93 

ii8-75 

18.82 



3.26 
18.19 



Lot 2, Fed 

on Hay 
and Maize 



Kgs. 

98.61 
118.56 

19-95 



1. Si 
19.20 



Lot 2, receiving maize, produced about the same gain relatively 
to the digestible matter consumed as Lot 1, notwithstanding the 
smaller amount of protein supplied. A block test tended to show a 
slight superiority on the part of Lot 2. Subsequent experiments * 
gave confirmatory results, barley being compared with beans on one 
animal each. The following table shows the actual digestible nu- 
trients, computed per 1000 kilograms live weight, and the total gain 
for each period : — 



Table 75. — Influence of Protein Supply on Gain by Mature Fat- 
tening Sheep 





Number 
of Days 


Sheep No. i, Fed on Barley 


Sheep No. 2, Fed on Beans 


Period 


Total 
Gain 


Digested per iooo 

Kilograms Live 

Weight 


Total 
Gain 


Digested per iooo 

Kilograms Live 

Weight 




Protein 


Total 

Nutrients 


Protein 


Total 
Nutrients 


III . . . 

IV . . . 

V . . . 


29 
20 
38 


Kgs. 

1.6 
1.4 
4.0 


Kgs. 

1.62 
1.63 
2.03 


Kgs. 

14.69 

I5-23 
17.32 


Kgs. 

2.4 
0.9 
3-6 


Kgs. 

3-13 
2-95 
3.61 


Kgs. 

16.12 
16.02 
16.32 


Total . 


7.0 


6.9 





1 Landw. Jahrb., 25 (1896), 175. 



THE FATTENING OF MATURE ANIMALS 



367 



In the final period of an experiment by Weiske with lambs cited 
in Chapter XI (487) the animals, when two years old, received an 
exclusive hay ration from which they digested 1.22 lb. of protein 
per 1000 pounds live weight. While no material fattening was pos- 
sible on such a ration, there was still a gain of protein nearly as great 
per head as in earlier periods, thus rendering it probable that the pro- 
tein supply was at least nearly sufficient for a moderate rate of 
fattening. 

The foregoing results indicate that 1.5 lb. of digestible protein 
per day and 1000 pounds live weight is at least sufficient for 
mature fattening sheep, while the experiments on cattle about to be 
mentioned suggest that the amount might even be reduced consider- 
ably below this limit. 

Cattle. — In Kellner's respiration experiments upon fattening 
cattle (443) , rations containing comparatively small amounts of protein 
produced as satisfactory a rate of fattening as those richer in that 
nutrient. Dividing the experiments into five groups according to 
the amount of digestible crude protein consumed gives the following 
averages : — 

Table 76. — Influence of Protein Supply on Gain by Mature Fat- 
tening Cattle 





Number 
of Ex- 
peri- 
ments 


Aver. 

Live 

Weight 


Rations per iooo 
Kgs. Live Weight 


Gains per iooo 
Kgs. Live Weight 


Group 


Digestible 
Protein 


Metaboliz- 

able 

Energy 


Protein 


Fat 


Com- 
puted 
Energy 


I . . . 

II . . . 

III . . . 

IV . . . 

V . . . 


7 

14 
18 
11 
10 


Kgs. 
656 

651 
667 
671 
691 


Kgs. 

0.523 
0.745 
I.069 

1-332 
2.168 


Therms 

31-54 
33-89 
34-50 
35-32 
43-36 


Grams 

87.2 

82.3 

I3I-0 

154.0 

i57-o 


Grams 
610.1 
619.8 
661.O 

756.8 
754-o 


Therms 
6.29 
6.36 
7-03 
8.07 
8.06 



The greater gains obtained in the experiments in which the larger 
amounts of protein were fed are not to be ascribed to this fact but to 
the greater consumption of total feed, since it has been shown that 
protein is no more available than non-nitrogenous nutrients for fat 
production. The point of the comparison is that rations containing 
amounts of protein little if at all greater than the maintenance require- 
ment gave relatively quite as large gains per unit of energy supplied 
as did those containing three or four times as much protein. 



3 68 



NUTRITION OF FARM ANIMALS 



The periods having been short in these experiments, the gain in 
live weight cannot be satisfactorily determined, but on the basis of 
Lawes and Gilbert's determinations of the composition of the increase 
(442) it may be estimated to have been approximately one pound per 
day. 

Loges 1 reports the results of experiments undertaken at Pomritz 
to test Kellner's conclusions, in which a nutritive ratio of i : 10.3 gave 
as great gains in weight with mature cattle as one of 1 : 5.7, but the 
absolute amounts of protein consumed are not stated in the abstract. 

Apparently from 0.75 to 1 lb. of digestible protein per 1000 
pounds live weight is sufficient to meet the requirements of fully 
mature fattening cattle. 

Swine. — Such experiments on the fattening of mature swine as 
are on record show that these animals, like cattle and sheep, need at 
most but a comparatively small surplus of protein over the amount 
necessary for maintenance. 

The respiration experiments by Meissl, Strohmer and Lorenz upon 
the sources of fat by swine (443) afford a general illustration of this. 
The following table shows the digestible protein and the metaboliz- 
able energy of the feed and the gain of energy by the animal. No 
distinct superiority of the high protein ration of Experiment IV over 
the low protein rations of Experiments I and III appears, while the 
greatest gain was realized in Experiment II with a moderate protein 
supply but relatively high energy content. 

Table 77. — Influence of Protein Supply on Gain by Mature Fat- 
tening Swine 



Animal 



I . 
II 
III 
IV 



Live 
Weight 



140 
70 

125 
104 



Rations per 100 
Pounds Live Weight 



Digestible 
Protein 



Lb. 

0.074 
0.161 
0.098 
0.410 



Metaboliz- 

able 

Energy 



Therms 

5-n 

IO.02 

4.10 

3-94 



Gain of Energy 



Per 100 Lb. 
Live Weight 



Therms 

2-54 
5-96 
1.48 
2.56 



Per Therm 

Metaboliz- 

able 

Energy 



Therms 
O.50 
O.58 
O.36 
0.43 



Soxhlet,in his experiments on the same subject (442), fed two swine 
16 months old and weighing about 200 pounds each at the beginning 

1 Centbl. Agr. Chem., 31 (1902), 646. 



THE FATTENING OF MATURE ANIMALS 



369 



of the experiment, a low protein ration consisting exclusively of rice 
for 75 and 82 days, respectively. The protein content of the ration 
and the average daily gain in live weight per head were as fol- 
lows : — 

Table 78. — Influence of Protein Supply on Gain by Mature Fat- 
tening Swine 



II 
III 



Initial Live 
Weight 



Lb. 

220 
213 



Digestible Protein (N X 6.25) 



Per Day and 
Head 



Lb. 

O.265 
O.269 



Per Day and 

100 Lb. Live 

Weight 



Lb. 

O.I2I 
O.I26 



Daily Gain 

in Live 

Weight per 

Head 



Lb. 

I- 15 

1.04 



These few results upon mature swine are of interest as showing the 
possibility of considerable fattening on low protein rations. In prac- 
tice the results are of comparatively little significance since the com- 
mercial fattening of swine is usually carried out upon the immature 
animal. 



The recorded experiments show that in the fattening of 
mature animals as satisfactory results have been obtained with 
rations containing 0.75 to 1.5 pounds of digestible protein per 
1000 pounds live weight as with those containing a much more 
abundant supply. Even these amounts, however, are from 
50 to 100 per cent higher than is necessary for maintenance, 
but with the exception of a small group of Kellner's experi- 
ments in which approximately the maintenance requirement 
of protein was consumed the results fail to show whether it is 
practicable or advisable to reduce still further the protein con- 
tent of fattening rations. As regards the simple question of 
protein supply, it appears likely that an amount of this nutrient 
but little superior to the maintenance requirement is all that is 
absolutely necessary. In practice, however, the inferior digesti- 
bility of low-protein rations (723, 724) as well as the fact that 
such rations are likely to be less palatable than those furnishing 
a more liberal supply have to be considered. The simple ad- 
dition of non-nitrogenous nutrients to a maintenance ration 



2 B 



370 NUTRITION OF FARM ANIMALS 

might furnish ample material for the production of body fat 
and yet not convert it into a practicable fattening ration. The 
economic aspects of the question, however, will be considered 
in connection with the subject of meat production (Chapter 
XII), the present chapter dealing more especially with the 
physiological aspects of the fattening process. 






CHAPTER XI 
GROWTH 

§ i. General Nature of Growth 

457. Cell multiplication. — The animal originates in a single 
microscopic germ cell. Its advance from this insignificant 
beginning to the size and complexity of maturity is effected 
by a multiplication of the number of cells, together with a 
progressive differentiation of function, the whole constituting 
the process of growth. Growth, then, may be characterized 
briefly as consisting in an increase of the structural elements of 
the body, chiefly by cell multiplication, resulting in a gain in size 
and weight. 

The increase during growth 

458. Composition of increase. — As with fattening animals, 
so in a study of the feed requirements of growing animals, a 
prime factor to be considered is the amount and composition 
of the gain made at different ages. The nature of the gain 
made during growth may be investigated either by means of 
comparative slaughter tests or by means of respiration experi- 
ments. Of the former there are on record a study by Wilson l 
on the growth of pigs for the first 16 days after birth, an inves- 
tigation by Tschirwinsky 2 on pigs between the ages of 2 and 6 
months, one by Kern and Wattenberg 3 on the growth of lambs 
between the ages of 6 and 28 months, one by Jordan 4 upon the 
growth of cattle between the ages of 23 and 33 months and one 
by Wellmann 5 on young pigs. Data regarding dogs and cats 
are also on record in investigations by Thomas 6 and by Gerhartz. 7 

1 Amer. Jour. Physiol., 8 (igo3), 197. 2 Landw. Vers. Stat., 29 (1883), 317- 

3 Jour. Landw., 28 (1880), 289. 

4 Maine Expt. Sta., Rpt. 1895, Vol. 2, pp. 36-77. 

5 Landw. Jahrb., 46 (1914), 499. 

6 Arch. (Anat. u.) Physiol., 191 1, p. 9. 

7 Arch. Physiol. (Pfluger), 135 (1910), 163. 

371 



372 



NUTRITION OF FARM ANIMALS 



Respiration experiments by Soxhlet 1 on three young calves 
included determinations of the gain or loss of ash, while the 
live weights of the animals are also recorded. The feed being 
exclusively milk, the variations in the contents of the digestive 
tract were probably slight and a computation of the composition 
of the increase based upon the live weights seems justified. 

The results of both the slaughter and respiration experiments 
are contained in the following table, the energy content being 
computed from the fat and protein. 

Table 79. — Composition of Increase or Live Weight in Growth 











Composition of Increase 






Designation of 
Animal or Period 


Species 
of Ani- 


Aver- 
age 
Age 




fc 


Author 










° 5 






mal 


Days 


Water 


Ash 


Pro- 
tein 


Fat 


















w £ 










% 


% 


% 


% 


Cals. 




Skim milk "j 


( 


8 


80.08 


0.03 2 


18.40 


1.49 


540 


Wilson . . . • 


Lactose | 


Swine \ 


8 


78.91 


1.42 2 


17.92 


i-75 


529 


. 


Dextrose J 


I 


8 


79-44 


1.62 2 


i7-3o 


1.64 


518 


■ 


VIII 1 


Swine < 


37 


75-53 


1.92 


I5-52 3 


7-03 


698 


Wellman . . 


IX | 


42 


76.86 


2.00 


15.18 3 


5-96 


643 






[ 


4 


67.96 


I.84 


I3-o8 3 


17.12 


1055 


Thomas . . 





Dog 


16 


64.01 


2.52 


16.63 3 


16.84 


1151 




- — ■ 


54 


72.84 


2.89 


I7-59 3 


6.68 


736 







I 


IOI 


66.56 


4.49 


22.31 3 


6.64 


818 







f 


4 


80.61 


I.63 


11.66 3 


6.10 


544 


Thomas . . 





Cat 


18 


68.29 


2-73 


18.93 3 


10.05 


935 







I 


IOI 4 


64.16 


3-52 


24.01 3 


8.31 


982 


Gerhartz . . 





Dog 


10 


72.93 


2.90 


13-98 3 


10.20 


800 


■ 


C ) 


f 


8 


62.55 


3-35 


19.24 


14.86 


1136 


Soxhlet . . . ■ 


B. 1 


Calf \ 


15 


61.28 


3-63 


19.15 


15-94 


1182 


. 


B. 2 


1 


21 


62.13 


3-50 


17-15 


17.22 


1 186 


Tschirwinsky . j 


No. 3 \ 

No. 2 J 


Swine I 


114 


46.51 


3-73 


9.10 


40.66 


1988 


134 


34-23 


2.24 


9-73 


53 .80 


2570 




Lot I: 


Sheep 














" 






Periods I and II 




290 


43-84 


11.31 6 


44-85 


2226 




Periods III and IV 




521 


27.27 


7.03 6 


65.70 


3014 


Kern and Wat- • 


Period V 




744 


22.18 


5.72 s 


72.10 


3255 


tenberg . . 


Lot II : 


Sheep 














Periods I and II 




290 


38.41 


9.91 B 


51.68 


2484 


■ 


Period III 
Average 


Cattle 


458 
840 


16.03 


4-13 6 
13-57 


79-84 
40.60 


3547 


Jordan 6 . . 


39.65 6.18 


2100 



1 i er Ber. Versuchs-Station Wien, pp. 101-155. 2 By difference. 

3 Fat- and ash-free dry matter. 4 Two periods. 

5 Computed from " fat-free body." 

6 The figures differ slightly from those reported by the author. 



GROWTH 



373 



In spite of irregularities and gaps in the table two general 
facts are clearly shown ; first, that the percentage of water in 
the gain decreases and that of dry matter increases with ad- 
vancing age of the animal, and second, that of the dry matter 
gained, an increasing proportion is fat as the animal matures. 
The latter fact becomes especially clear if the composition of 
the dry matter of the ash-free gain be computed. 

The result of investigations by Waters, Mumford and Trow- 
bridge as reported by Henry and Morrison x are quite in accord 
with the teaching of Table 79, the percentage composition of 
the first and the second 500 pounds gained by young fattening 
steers being as follows : — 



First 500 lb. 
Second 500 lb. 



Water 


Ash 


Protein 


% 
37-6 
17.8 


% 
2.0 

i-5 


% 
II.Q 

5-2 



Fat 



% 
48.6 

75- 



459. Energy content of gain. — The amount of energy 
stored in a unit of increase in live weight shows a fairly regular 
and notable increase as the animal grows older, due to the 
smaller percentage of water and the higher percentage of fat 
which it contains. The rate of increase in the energy content 
per unit in those cases in which no considerable fattening of the 
animal was attempted seems to be fairly regular up to about 3.0 
Therms per pound and the same thing is also true of most of the 
results upon fattening animals up to about 3.5 Therms per 
pound, although the actual energy content per unit,at the same 
age is naturally greater in the fattening animal and the limit is 
therefore reached earlier in life. In both cases the limit seems to 
correspond in a general way with the average energy content of 
the gain made by mature fattening animals as estimated in 
Chapter X (451), viz., about 3.25 Therms per pound. The data, 
however, are few and further investigation is much to be desired. 



Relation of growth to age 

460. The rate of growth. — If the successive weights or 
dimensions of a growing animal be platted, there are obtained 

1 Feeds and Feeding, 15th Ed., p.84. 



374 NUTRITION OF FARM ANIMALS 

what might be called the curves of weight or of stature. These 
rise rapidly at first and afterwards more slowly as the animal 
approaches maturity. Or in like manner the increments of 
weight or size observed in successive equal periods (day, week, 
month or year) may be platted, showing at what periods the 
absolute growth is most rapid. 

It is evident, however, that an increase of a pound in weight 
by an animal weighing 500 pounds is relatively much less than 
the same increase in a 100-pound animal. For many purposes, 
a better expression of the relation of growth to age is afforded 
by a computation of the rate of growth, by which is meant the 
increment in a given unit of time expressed as a fraction of the 
amount present at the beginning of that time. Thus in the 
instance just supposed the rate of growth in weight per day 
would be in the first case one five-hundredth and in the second 
one one-hundredth. In the second case the small animal, in 
proportion to its weight, is growing five times as fast as the 
larger and may be regarded as showing five times the energy 
of growth. An evident advantage of this manner of expression 
is that it permits of a comparison between animals of very dif- 
ferent weights, as, for example, of sheep with cattle. 

461. Rate of growth at different ages. — Somewhat ex- 
tensive observations, both on man and the lower animals, show 
that the rate of growth as just defined diminishes from birth 
onward, the diminution being more rapid at first and slower 
as maturity is approached. This subject has been discussed in 
a most illuminating manner by Minot 1 on the basis of his own 
and others' observations on guinea pigs, rabbits, chicks and 
other animals as well as on man. Graphically the rate of 
growth is expressed by a descending curve, steep at first, but 
gradually becoming more and more nearly horizontal, while 
the same curve extends backward without material break 
into intrauterine life. Foster says: "It seems as if the im- 
petus to growth given at impregnation gradually dies out." In 
the early stages of growth, therefore, the anabolic processes, 
which tend to build up tissue, predominate, while as time goes 
on the katabolic processes gain more and more over the 
anabolic until at maturity the two tend to become substantially 
balanced. 

1 C. S. Minot : Age, Growth and Death, Chapter III. 



GROWTH 375 

462. The measure of growth. — The most familiar and 
obvious measure of growth is the increase in size or weight of 
the body. While for many purposes this is an entirely adequate 
standard, it is not a strictly accurate expression of growth proper. 

In the first place the facts regarding the composition of the 
increase in growth which have just been considered render it 
evident that a unit of gain in live weight has a very varying 
significance. In the very young animal as much as 80 per cent 
of it may consist of water, while its dry matter is chiefly 
protein. In the nearly mature animal, on the contrary, its 
percentage of water may fall to between 30 and 40, while its 
dry matter consists largely of fat. Moreover, a surplus of feed 
over the maintenance ration may lead to a deposition of fat 
in the young as well as in the mature animal, resulting in a 
greater increase in weight than that due to normal growth. 
On the other hand, as was shown in Chapter VIII (372), growth 
in the sense of increase in size may continue on a ration barely 
sufficient or even insufficient to maintain a stationary weight, 
i.e., growth when expressed in terms of weight may be masked 
by a loss of fat. 

The essential structural elements of the body, the increase 
of which constitutes growth proper, consist (aside, of course, 
from water) mainly of protein and mineral matter (98). Growth, 
therefore, in this view of it, is equivalent to a gain by the body 
of protein and ash, especially the former. The increase of 
protein, therefore, may be regarded as constituting a more 
accurate measure of growth in the narrower sense than mere 
increase in weight. 

463. Rate of increase of protein. — What is true of the 
weight or size of the growing animal is true also of growth in the 
somewhat narrower sense of increase of protein tissue. 

The writer has elsewhere 1 collated the results of a number 
of experiments, including those whose results regarding the com- 
position of the increase are recorded in Table 79, in which the 
gain of protein by growing animals has been determined with 
more, or less accuracy. In addition the results of experiments 
by Fingerling 2 on calves, of Ostertag and Zuntz 3 upon pigs, 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), pp. 13-17. 
2 Landw. Vers. Stat., 68 (1908), 141 ; 76 (1912), 1. 
3 Landw. Jahrb., 37 (1908), 231. 



376 



NUTRITION OF FARM ANIMALS 



and of Just 1 on lambs have been included in the table which 
follpws. 

In those cases in which the experiments were made by the method 
of comparative slaughter tests, the composition of the control animals 
gives an approximate measure of the initial protein content of the 
body. When no control animal was analyzed the initial protein con- 
tent has been estimated as well as possible from the live weight. 
Since this was the case in the majority of the experiments it seems 
desirable also to compute the gain of protein per iooo live weight. 
Except in the case of very young or very fat animals, the results are 
likely to correspond substantially with those computed in the other 
way, while they have the advantage of being expressed in the manner 
usually .adopted for formulating feeding requirements. 

Table 80. — Rate of Gain of Protein 



Average Age 



Days 



Daily Gain of Protein 



Per ioo Body 
Protein 



Per iooo Live 
Weight 



Cattle 

Soxhlet . . . 

Soxhlet . . . 

Soxhlet . . . 

Soxhlet . . . 

Fingerling . . . 

Soxhlet . . . 
De Vries Jzn 

De Vries Jzn . . 

Neumann . . . 

Neumann . . . 

De Vries Jzn . . 

Fingerling . . . 

De Vries Jzn . . 

Neumann . . . 

Neumann . . . 

Neumann . . . 

Neumann . . . 

De Vries Jzn . . 

De Vries Jzn . . 

De Vries Jzn . . 

Fingerling . . . 

Neumann . . . 

De Vries Jzn . . 



15 

18 
21 
21 
32 
37 
38 
40 

45 
45 
47 
5o 
50 
54 
57 
62 

63 
64 

65 
68 
69 
74 



2-347 
2.076 
1.644 
1.722 
1.974 
1.693 

1-335 
1.246 

i-795 
1.449 
1.272 
1.248 
0.880 
1.082 
1.026 
1.320 

o-939 
0.678 
0-655 
1.020 
0.948 
1.062 
0.713 



3-994 
3-552 
2.803 
3.024 
3.085 

2-755 
2.276 
2.124 

2-945 
2.419 
2.169 
2. 161 
1.500 
1.844 

2.284 
1.611 
1.209 
1.209 
1.723 
1.7*19 
1.823 
1. 271 



1 Landw. Vers. Stat., 69 (1908), 393, results of periods 3, 5, 7 and 9. 



GROWTH 



377 



Average Age 
Days 



Daily Gain of Protein 



Per ioo Body 
Protein 



Per iooo Live 
Weight 



Cattle 
De Vries Jzn . . . . 

Fingerling 

Fingerling 

Fingerling 

Fingerling 

Jordan 

Sheep 

Weiske 

Weiske 

Weiske 

Weiske 

Just 

Kern and Wattenberg . 

Weiske 

Just 

Weiske 

Just 

Weiske 

Just 

Weiske 

Weiske 

Kern and Wattenberg . 
Kern and Wattenberg . 
Kern and Wattenberg . 

Swine 
Ostertag and Zuntz 
Sanford and Lusk . . 
Wilson . . . . . 

Ostertag and Zuntz 
Ostertag and Zuntz 
Ostertag and Zuntz 
Tschirwinsky .... 
Tschirwinsky . . . 

Dog 

Thomas 

Gerhartz 

Thomas 

Thomas 

Thomas 

Cat 

Thomas 

Thomas 

Thomas 



ioo 
150 
182 
214 
297 
840 

140 
177 
214 

254 
285 
290 
293 
3i5 
328 
360 
366 
39o 
405 
43 6 
458 
521 
745 

Si 

7 
8 

13 

21 

26 
114 
134 

4 
10 
16 

54 
101 

4 

18 

101 



0.711 

0.48 

0.41 

°-33 
0.22 

0.064 

0.372 
0.307 
0.219 
0.288 
0.233 
0.272 
0.179 
0.182 
0.160 
0.180 
0.238 
0.158 
0.178 
0.033 
0.068 
0.087 
0.067 

5-553 
7.269 
6.852 
4.129 

1.840 

0-757 
0.442 
0.483 

5-94 
6.44 
6.71 
1.70 
1.82 

6.10 

5-89 
1.60 



1. 192 

0.83 

0.76 

0.64 

0.47 

0.089 

0.651 
0.499 
0.360 
0.449 

o.475 
0.303 
0.284 
0.370 
0.264 
0.360 
0.382 

0.315 
0.301 
0.061 
0.074 
0.096 
0.069 

9.029 
5.621 

5-757 
6.675 

3-257 
1.470 
0.663 
0.740 

7-73 
7.67 

8-73 
2-35 
2-93 

7-57 
7.91 

3-o5 



378 NUTRITION OF FARM ANIMALS 

It is obvious that the error in single results obtained in this 
way may be very considerable, but the general teaching of the 
table is perfectly clear, viz., that the rate of growth of protein 
tissue, like the increase in size or in weight, whether expressed 
per unit of body protein or per iooo live weight, is relatively 
high in the new-born animal and decreases rapidly at first and 
more slowly later, tending to be asymptotic to the zero line. 

Letting the g equal the gain of protein per day per iooo live 
weight and a the age in days, a curve represented by the em- 
pirical equation 1 




corresponds fairly well with the general average of the observed 
results on cattle and sheep. With swine, the few results ap- 
pear to indicate a greater rate of growth during the first three 
months. This is shown clearly in the accompanying graph 
(Fig. 38) in which the individual results on the different species 
are shown by the light lines, while the heavy curve is that repre- 
sented by the foregoing equation. Of course considerable 
individual variations are to be expected, and no particular 
significance attaches to the mathematical form of the curve, but 
it would seem that this formula may be used tentatively to 
express in a broad general way the average rate of protein 
growth of farm ruminants at different ages. The few results 
on the dog and cat seem to indicate a higher rate of growth 
in the young of these species. 

464. Rate of gain of energy. — While the rate of increase 
of protein, as discussed in the foregoing paragraphs, may be 
regarded as the measure of growth in the more restricted sense, 
and while it is of importance as an indication of the amount of 
protein which must be supplied in the feed, the actual gain in 
normal growth includes more or less production of fat, as is 
clearly shown by the data regarding the composition of the in- 
crease already considered (458). Growth, therefore, in practice 
involves a storage of energy in the body not merely in the pro- 
tein gained but also in the accompanying fat laid on, while it 
is difficult to draw an exact line between the growth and the 
fattening of young animals. 

1 The equation of a rectangular hyperbola. 



GROWTH 



379 



If/OOO/ -<«rf m 







































s 










































































i 










U 


























1 












3 

I 




























■s 








^ ft 


-*> 

e 

l! 




































li 


il 




























1 










































































<} 






































•^ 

% 






































*1 












































































i 




































| 


<3 




































P 


1 

F> 




































i 








































4 


































#1 

' I 

/ 






































/ 






























£ 














— 


— -. 








<* g 


3 • 


i I 






a i 


» > 




! < 


^ — 


h 


1 


s — 


3 


* 


r> 


l ! 


'' 





XI 



> 

c/i 

O 

a 

o 
o 
o 






00 
CO 



o 

I— I 



3 8o 



NUTRITION OF FARM ANIMALS 



If it may be assumed that in those of the experiments re- 
corded in Table 79 in which no considerable fattening was at- 
tempted the increase in weight was approximately that due to 
normal growth, the amount of energy contained in the increase 
and the daily rate of gain of energy per 1000 pounds live 
weight may be computed. The following table shows the 
results of such a comparison, the figures per 1000 pounds 
being computed in direct proportion to the weight. 



Table 81. — Energy Content of Daily Growth 



Experimenter 



Thomas 

Thomas 

Wilson 

Soxhlet 

Gerhartz 

Soxhlet . . ... . 

Thomas 

Thomas 

Soxhlet 

Wellmann . . . . 
Wellmann . . . . 
Thomas . . . 

Thomas 

Thomas 

Tschirwinsky . . . 
Tschirwinsky . . . 
Kern and Wattenberg 
Kern and Wattenberg 
Lawes and Gilbert 
Lawes and Gilbert 
Kern and Wattenberg 
Kern and Wattenberg 
Kern and Wattenberg 
Jordan .... 
Lawes and Gilbert 



Animal 



Dog 

Cat 

Pig — Average 

Calf 

Dog 

Calf 

Dog 

Cat 

Calf 

Pig 

Pig 

Dog 

Dog 

Cat 

Pig 

Pig 

Sheep, Lot I 

Sheep, Lot II 

Pig 

Sheep 

Sheep, Lot II 

Sheep, Lot I 

Sheep, Lot I 

Cattle 

Cattle 



Average 
Age 



Days 

4 
4 



10 

15 

16 

18 

21 

23 

34 

54 

101 

101 

114 

134 

290 

290 

300 : 

456 l 

458 

521 

745 

840 

1460 ! 



Average 

Live 
Weight 2 



Lb. 
0.79 
0.38 
4.12 

106.87 
0.98 

138.60 

i-55 

0.864 

i5i-53 

13-52 

17-93 

3-38 

5-95 
1.91 

39-51 
34.66 
67.02 

73-42 
181.88 
135.58 
106.70 
102.51 
130.07 
826.10 
1272.40 



Energy Content 
of Growth 



Per Head 



Cals. 

58.13 
14.67 

73-58 
2634.00 

49-31 

3 I 53-°° 

113.40 

39.20 

3294.00 

243-9 

316.5 

38.02 

73-Q4 
27-34 
568.6 
705.6 
328.0 
608.1 
5041.0 

1185.4 
712.9 

434-5 

520.4 

1618.0 

6378.0 



Per 1000 
Lb. Live 
Weight 



Therms 
73-35 
38.47 
17.87 
24.66 

5Q-47 
22.74 

73-35 
45-36 
21.74 
18.04 

17-65 
11.25 

12.28 
14.32 

14-39 

20.36 

4.90 

8.28 

27.72 

8.74 
6.68 
4.24 
4.00 
1.96 
5.01 



Approximate. 



2 All data refer to empty weight, exclusive of hides. 



GROWTH 381 

The rate of gain of energy as thus computed is notably 
greater for young carnivora (dogs and cats) during the first two 
or three weeks than that of pigs or calves. Aside from this, the 
results on farm animals, although more or less irregular, present 
in general the same picture as those on the rate of gain of pro- 
tein, viz., a diminishing energy of growth with advancing age. 
The few instances showing a wide divergence from the majority 
may probably be assumed to be due to rapid fattening. 

§ 2. The Utilization of Feed in Growth 

The utilization of protein 

465. Relative values of proteins for growth. — A considera- 
tion of the utilization of protein in growth necessarily raises 
the question of the relative values of different individual pro- 
teins in this respect. 

As was pointed out in Chapter IX (398), it appears probable 
that the protein requirement for maintenance is essentially 
an amino acid requirement and that the relative values of 
proteins for maintenance may prove to depend largely or wholly 
on their ability to supply certain specific " building stones " 
required for the performance of specific functions. In the 
growing animal there is, in addition to this requirement for 
functional purposes, a demand for amino acids out of which 
new body proteins may be built up. In growth, therefore, the 
amino acid requirements may differ from those for maintenance 
not only in being quantitatively greater but in being qualita- 
tively different. A striking illustration of this is afforded 
by the investigations of Osborne and Mendel 1 on the relation 
of lysin to growth. 

In common with other investigators they have found that trypto- 
phan is indispensable for maintenance (399). Wheat gliadin con- 
tains tryptophan but only a minute amount of lysin. While they 
have repeatedly secured maintenance for long periods on rations con- 
taining gliadin as the sole protein, they have been unable to secure 
growth with such rations, but the simple addition of lysin enabled 
growth to proceed at a normal rate. The body proteins contain lysin, 
ox muscle, for example, yielding 7.6 per cent (50). Evidently this 

1 Jour. Biol. Chem., 12 (1912), 473; 17 (1913), 325; 26 (1916), 293. 



382 NUTRITION OF FARM ANIMALS 

amino acid cannot be synthesized in the body but must be supplied 
in the feed in order to permit the construction of the new protein 
molecules in the tissue, while for maintenance (399) it appears to be 
dispensable. Moreover, they have shown that the addition to in- 
adequate proteins like gliadin of other proteins containing lysin per- 
mits growth to take place and furthermore that the proportion of the 
second protein which must be added in order to support normal 
growth is less in proportion as it is richer in lysin. 

Osborne and Mendel's conclusions have been strikingly confirmed 
by the results obtained by Buckner, Nollau and Kastle x from feeding 
young chicks grain mixtures of high and low lysin content. 

It appears that the lack of lysin in a protein renders it in- 
capable of supporting growth, although it may still be adequate 
for maintenance (399), and that the proportion of lysin in those 
proteins containing it constitutes a limiting factor for the 
amount of growth which they can support. Tryptophan is 
obviously another limiting factor in this respect, while it must 
be regarded as altogether probable that other amino acids 
belong in the same category and may become limiting factors 
if the supply of them is deficient. In other words, the amount 
of some particular amino acid which is available may become 
the minimum factor which determines the rate of growth, just 
as the minimum supply of potassium, for example, may deter- 
mine the rate of growth of a crop. The unsatisfactory results 
obtained in practice with maize as the sole feed for young 
animals may well be due in large part to the poverty of the 
mixed proteins of this grain in tryptophan and lysin, it having 
been shown that as the sole source of protein they can support 
but slow growth (783). 

Unfortunately the knowledge available on these points is as 
yet chiefly qualitative in character and affords no sufficient 
foundation on which to base a quantitative discussion of the 
relative values of proteins in farm practice. Accordingly, in 
the case of growth as in that of maintenance it appears neces- 
sary for the present to consider questions regarding the protein 
requirement upon the basis of total protein, largely irrespective 
of its nature. (Compare Chapter XVII, § 4.) 

466. Percentage retention of feed protein. — In the mature 
animal, the katabolism of protein substantially keeps pace 

1 Amer. Jour. Physiol., 39 (1915), 162. 



GROWTH 



383 



with the supply in the feed (402), as indeed is really implied 
in the conception of maturity. By a mature animal is meant 
one which has completed its growth, and growth consists essen- 
tially in an increase of the nitrogenous structural elements 
of the body. Obviously, therefore, if the capacity for growth 
has been exhausted, no material storage of protein can occur 
and an excess of this material above the maintenance require- 
ment will serve chiefly or wholly as a source of energy to the 
organism. 

With the young animal the case is different. Its rapidly 
growing cells and tissues demand a liberal supply of protein, 
and if this is afforded by the feed it is largely utilized to build 
up tissue instead of undergoing nitrogen cleavage. Conse- 
quently, other things being equal, a much larger percentage of 
the feed protein is retained in the body. 

The investigations whose results have been considered on previous 
pages (463), especially those upon the younger animals, afford striking 
illustrations of this fact, Soxhlet's experiments upon calves being the 
earliest and most familiar. Their results are summarized in the fol- 
lowing table, the feed consisting of fresh whole milk ad libitum. 

Table 82. — Percentage of Feed Protein Retained — Soxhlet 



Animal 



A 
B 

C 



Age 


Digested 
Protein 
of Feed 
per Day 


Daily 

Gain of 

Protein 

by Animal 


Days 


Grams 


Grams 


f 16-19 


I7I-3 


129. 1 


} 30-33 


228.4 


163.6 


15 


330-8 


231.8 


21 


317.5 


216. 1 


8 


262.4 


202.0 



Digested 
Protein 
Retained 



Per Cent 

75-3 
71.6 
70.1 
68.1 
77.0 



More recent and even more striking illustrations of the same fact 
are afforded by Fingerling's experiments. Thus, in one instance 
a calf averaging 9 days old received whole milk and in a succeed- 
ing period milk with the addition of butter fat and lactose, and 
retained the percentages of digested protein shown in the following 
table. 



3^4 



NUTRITION OF FARM ANIMALS 



Table 83. — Percentage of Feed Protein Retained — Fingerling 



Period 


Age 
(Average) 


Digested 
Protein 
of Feed 
per Day 


Daily 

Gain of 

Protein 

by Animal 


Digested 
Protein 
Retained 


I 


Days 

9 
19 


Grams 
249.42 
254-.94 


Grams 
214.38 
207.48 


Per Cent 
86.0 


II 


81.4 





With advancing age, a relatively smaller retention is observed. 
Thus Neumann obtained for calves 40 to 70 days old percentages vary- 
ing from 38.7 to 48.3, and Tschirwinsky, experimenting on pigs 100 
to 120 days old, observed a retention of 20.7 to 33.6 per cent of the 
digested protein. With still older animals a yet smaller percentage 
retention has been observed, diminishing to nearly zero with fully 
mature animals. 

467. Does not measure utilization. — On the basis of this 
greater percentage retention it has been customary to say that 
the utilization of feed protein is high in the case of the young 
animal and diminishes rather rapidly as it grows older. This 
statement is made essentially from a commercial standpoint 
and in that sense it is true. Only the growing animal is capable 
of using any large amount of feed protein to increase its stock 
of body protein and the ability to do this is the more marked 
the younger the animal. 

The percentage retention of the feed protein, however, is 
necessarily variable and neither affords a measure of the effi- 
ciency with which the animal converts it into body protein 
nor permits a comparison of that efficiency at different ages. 
The comparison is disturbed by two important factors to which 
attention has been especially called by Fingerling, 1 viz., the 
influence of the total amount of protein supplied and the effect 
of a deficient energy supply. 

468. Influence of protein supply. — As has already been 
implied, growth is primarily dependent upon biological factors. 
The feed supplies material for growth but does not determine 
its maximum rate. The rate of increase of protein as formu- 
lated in the previous section (463) represents (so far as the 
results are trustworthy) the capacity of the animal for protein 

1 Landw. Vers. Stat., 74 (1910), 1. 



GROWTH 



38S 



storage at different ages, but the percentage of the feed protein 
which is retained will depend upon the relation between this 
capacity and the amount of protein actually supplied. For 
example, suppose a calf weighing 100 pounds to be capable of 
storing up per day 0.25 pound of protein and to require 0.05 
pound for maintenance. If it receives 0.35 pound digestible 
protein in its feed and is able to store up the maximum amount 
of 0.25 pound on this ration, 71.4 per cent of the digestible 
protein would be retained, while 28.6 per cent would katab- 
olize and its nitrogen excrete in the urine. But if the feed 
of the animal supplied 0.45 pound digestible protein, the gain 
would still be 0.25 pound, since this is the maximum possible 
for the animal, but the percentage of the feed protein retained 
would be only 55.6, while 44.6 per cent of it would be katab- 
olized. The organism is unable to use the added one-tenth 
pound for constructive purposes and therefore it is katabolized 
as shown in Chapter IX (402-404) and serves simply as a source 
of energy. In other words, the greater the excess of protein 
supplied in the ration over the minimum required by the de- 
mands of growth and maintenance, the lower will be the per- 
centage retained in the body. On the other hand, with rations 
deficient in protein the percentage retention will increase with 
the protein supply up to the minimum amount necessary to 
utilize the growth capacity of the animal. 

Fingerling's experiments afford striking confirmation of the truth of 
the foregoing deductions from the general laws of protein katabolism. 

A calf received daily in one period 8 kgs. of whole milk with an 
addition of butter fat and lactose, while in the succeeding period 
whole milk alone was fed in amounts proportional to the age of the 
calf, averaging 11.875 kgs. per day. The results as regards protein, 
expressed in terms of nitrogen, were as follows : — 

Table 84. — Influence of Protein Supply on Percentage Retention 

of Nitrogen 



June 2-5 
June 25-30 



Digested 
Nitrogen 
of Feed 



Grams 
42.49 

62.97 



Urinary 

Nitrogen 



Grams 
7.91 

28.77 



Gain by 
Calf 



Grams 

34.58 
34.20 



Per Cent 
of Feed 
Protein 

Retained 



81.4 
54-3 



2 C 



3 86 



NUTRITION OF FARM ANIMALS 



Evidently the protein supply was sufficient in the first period to 
ensure normal growth. The additional supply in the second period, 
therefore, had no effect on the gain but simply increased the protein 
katabolism, i.e., the added protein was used as a source of energy for 
maintenance or for the production of fat. 

On the other hand, a supply of protein notably insufficient to per- 
mit normal gain may yet show a comparatively high percentage re- 
tention. Thus the same calf received in an intermediate period only 
4 kgs. per day of whole milk together with sufficient butter fat and 
lactose to supply the necessary energy. As compared with the first 
period only about one-half of the normal gain of protein was secured, 
yet the percentage retention is but slightly reduced. 



Table 85. — High Percentage Retention of Nitrogen on Insuffi- 
cient Protein 



June 2-5 
June 13-ii 



Digested 
Nitrogen 
of Feed 



Grams 
42.49 
19-95 



Urinary 
Nitrogen 



Grams 
7.91 
5-5 



Gain by 
Calf 



Grams 

34.58 

14.90 



Per Cent 
of Feed 
Retained 



81.4 
74-7 



469. Influence of deficient energy supply. — But not only 
may a surplus of protein be utilized as a source of energy in the 
manner just illustrated, but if the energy supply in the feed 
is inadequate protein may be diverted from growth to serve 
as fuel material, precisely as in the case of maintenance (412), 
thus lowering both the observed gain and the percentage re- 
tention. 



This effect is well illustrated by the following experiment by Fin- 
gerling upon a calf receiving in the first two periods a limited quan- 
tity (10 kgs. per day) of whole milk. As the animal grew older the 
energy supply became insufficient and protein was diverted to fuel 
purposes so that the actual gain and the percentage retention both 
diminished. When, in a third period, one-half of the milk was re- 
placed by butter fat, the protein supply being kept at nearly the 
same level by the addition of egg albumin, the actual gain rose nearly 
to its original level and the percentage retention became even higher 
than at first on account of the somewhat reduced protein supply. 



GROWTH 



387 



Table 86. — Influence of Energy Supply on Percentage Retention 

of Nitrogen 



Sept. 29-Oct. 1 
Oct. 7-9 . . 
Oct. 19-27 



Digested 
Nitrogen 
or Feed 



Grams 

51.84 
51-87 
45-76 



Urinary 

Nitrogen 



Grams 

12.62 

19.99 

8.10 



Gain by 
Calf 



Grams 

39.22 
31.84 
37.66 



Per cent 
of Feed 
Protein 

Retained 



75-7 
61.5 
82.3 



470. Meaning of utilization. — The percentage of the digest- 
ible protein of the feed which is retained in the body of the 
growing animal, then, is not in itself a measure of the efficiency 
of the animal organism in converting feed protein into body 
protein, since the proportion retained is affected both by the 
magnitude of the protein supply in the feed and by the energy 
content of the ration. What then is the correct conception of 
the utilization of the feed protein ? 

As appeared in the previous section, the amount of protein 
which a growing animal can store up seems to be a function of 
its age (463), and the attempt was made to formulate approxi- 
mately the capacity for growth in this sense at different ages. 
The percentage utilization of the feed protein in the physio- 
logical sense, as distinguished from the percentage retention, is 
the ratio between the body protein thus stored up and the least 
amount of feed protein in excess of the maintenance require- 
ment which is necessary to support this growth under the most 
favorable conditions, especially as to energy supply. Suppose, 
for example, that an animal three months old actually has the 
capacity, as computed by the formula on page 378, to store 
up daily 1.23 pounds protein per 1000 pounds live weight, and 
that it has been shown that it can just reach this capacity on 
a ration supplying 2 pounds of digestible protein per day. De- 
ducting 0.5 pound for maintenance (415), there remains 1.5 
pounds of protein in the ration out of which is produced 1.23 
pounds of body protein. The utilization is therefore 1.23 -f- 
1.5 = 82 per cent. If, on the other hand, it was found that 
2.5 pounds of protein had to be supplied in the ration in order 



3 88 



NUTRITION OF FARM ANIMALS 



to bring the gain of protein up to the capacity of the animal, 
the percentage utilization would be only 1.23 4- 2.0 = 62 per 
cent, while on the other hand if the maximum growth could 
be secured with 1.73 pounds of digestible protein, the utili- 
zation would evidently be 100 per cent. 

471. Experimental results. — The writer is not aware of 
any exact determinations of the percentage utilization in the 
sense just defined, that is, of the maximum amount of protein 
tissue which can be produced either from single proteins or from 
the mixed proteins of feeding stuffs, but interesting data regard- 
ing the utilization of protein by growing animals are furnished in 
experiments by Fingerling x upon calves and by Just 2 on lambs 
in which the influence of a varying protein supply upon the 
nitrogen balance was determined. 

Reckoning the maintenance requirement for protein at 0.5 
pound per 1000 pounds live weight, Fingerling's results for those 
periods in which the estimated capacity for growth appears to 
have been fully utilized were as follows : — 

Table 87. — Computed Utilization of Protein by Calves 



Animal 



B 
C 



H 



Period 



3 
1 
2 
4 
5 
Prelim- 
inary 
1-6 



Aver- 
age 
Age 
Days 



172 

175 

157 
184 
211 

237 
262 

309 

339 

135 

187 



Gain of Pro- 
tein PER 
IOOO 



Capac- 
ity for 
Gain 



O.70 
0.63 

O.76 
0.66 
O.58 

0.53 
0.48 
0.41 
0.38 
O.87 

O.05 



Ob- 
served 
Gain 



O.67 
O.63 
0.85 

o-75 
0.68 

o.57 
O.S4 
0.50 
0.44 

1.07 

0.80 



Feed Protein 
in Excess of 
Maintenance 

per IOOO 



True 
Protein 



1.94 
O.62 

2.15 
O.79 
2-59 
I.08 

1. 13 
O.31 
O.25 

2.42 
O.74 



Crude 
Protein 



2.00 
O.84 

2-44 
1.04 
2.85 

1.29 

i-37 
0.49 
0.42 

2.81 
1.01 



Percentage 
Utilization 



True 
Protein 



34. 
101, 

39^ 
94. 
26. 

52. 

47- 
161. 
176. 

44- 



108. 1 



Crude 
Protein 



33-5 
75-o 

34-8 
72.1 

23-9 

44.2 

39-4 
102.0 
104.8 

38.1 
79.2 



1 Landw. Vers. Stat., 76 (191 2), 1. 



Ibid., 69 (1908), 393. 



GROWTH 



389 



From these figures it appears that in the low protein periods 
the estimated capacity of the animals for growth was fully uti- 
lized with a surplus of digestible true protein over the maintenance 
requirement equal to or even less than that actually recovered 
in the growth, while a much larger supply of protein failed to 
secure any additional growth but simply forced up the protein 
katabolism. In other words, if the estimate for the maintenance 
requirement is approximately correct, the utilization of the 
digestible protein in the low protein periods must have ap- 
proached 100 per cent. Indeed, in at least two cases it is neces- 
sary to admit either that the estimate for maintenance is too 
high or that non-protein was used for maintenance. 



Table 



Computed Utilization of Protein by Lambs 













Feed Protein 










Ap- 


Gain of Pro- 


in Excess of 


Percentage 






proxi- 


tein PER IOOO 


Maintenance 


Utilization 







mate 






PER IOOO 










3 


Aver- 
age 
Age 

Days 












Animal 
















s 


Capac- 
ity for 
Gain 


Ob- 
served 
Gain 


True 
Protein 


Crude 
Protein 


True 
Protein 


Crude 
Protein 




I 


262 


O.48 


O.OI 


—O.09 


O.02 





50.O 




2 


280 


0.45 


O.40 


O.17 


o.54 


235-3 


74.I 




3 


296 


o-43 


O.48 


O.42 


0.56 


H4-3 


85.7 




4 


310 


0.41 


O.16 


—O.14 


O.26 


— 


6l.5 


I 


J 5 


3 2 4 


0.39 


O.36 


O.29 


O.44 


1 24. 1 


81.8 




6 


339 


0.38 


O.62 


O.27 


0.73 


229.6 


84.9 




7 


362 


0.36 


O.4O 


O.38 


0.52 


105.3 


76.9 




8 


377 


0.34 


O.24 


— O.22 


0.23 


— 


IO4.3 




9 


39i 


o-33 


0.34 


O.28 


O.42 


121.4 


81.O 




10 


407 


0.32 


-O.O3 


— 0.2I 


— O.II 


— 


— 


II 


( 1 


262 


0.48 


O.OO 


— O.II 


0.02 


— 


OO.O 


1 2 


280 


o.45 


O.32 


0.14 


0.49 


228.6 


65-3 




I 3 


296 


043 


O.47 


0.36 


0.52 


I30-5 


90.4 




1 4 


310 


0.41 


O.07 


—0.07 


0.37 


— 


18.9 




1 5 


324 


o.39 


O.38 


0.28 


0.42 


135-7 


90-5 


Ill 1 .... 


1 b 
7 


339 
362 


0.38 
0.36 


O.61 

o-33 


0.21 
0.42 


0.63 
0.57 


290.5 
78.6 


96.8 
57-9 




8 


377 


0.34 


0.24 


—0.22 


0.24 


— 


1 00.0 




9 


39i 


o-33 


0.29 


0.25 


0.41 


116. 


70.7 




10 


407 


0.32 


0.00 


—0.20 


-0.08 


— 


— 



1 Substituted for No. II. 



390 NUTRITION OF FARM ANIMALS 

Interesting data pointing in the same direction are contained 
in the investigation by Just, in which the nutritive value of 
non-protein for lambs was compared with that of protein. 
Estimating the maintenance requirement at 0.5 per thousand 
and computing the results of the protein periods as in Finger- 
ling's experiments, it appears that in nearly every case the 
actual gain of protein was only slightly less than the surplus of 
digestible crude protein above the maintenance requirement, 
while in many cases it was distinctly greater than the digestible 
true protein available. Apparently the non-protein must at 
least have contributed to the maintenance of the animal if not 
to its growth, while the utilization of the digestible true protein 
must have been very high (Table 88). 

Neither Fingerling's nor Just's investigations are adequate 
to solve the general problem of the maximum possible utiliza- 
tion of protein in growth, but their results indicate that it may 
be very high and should lead to caution in the interpretation of 
experiments upon the protein requirements for growth. 

Utilization of energy — net energy values for growth 

472. General conception. — The conception of net energy 
values for growth is entirely analogous to that of net energy 
values for maintenance or for fattening. They represent that 
portion of the feed energy supplied in excess of the maintenance 
requirement which the animal is able to store up in the gain 
made. It is important to keep this conception clearly in mind 
when considering the utilization of feed in growth and not to 
be misled by the greater economic efficiency of the young animal 
as a producer of live weight increase. 

It is a familiar fact that the young animal gains in weight 
relatively much faster than when more mature and this has 
led to the general impression that the young animal utilizes its 
feed more perfectly than the older animal, or in other words, 
that the net energy value of a feeding stuff for growth is greater 
than that for maintenance or for fattening. It is true that the 
gain in live weight is different in character in the young animal, 
containing more water and protein and less fat and therefore 
less energy (458, 459) , but on the other hand the results recorded 
in § 1 show a greater rate of growth as regards both protein and 



GROWTH 391 

energy (463, 464) in the young animal as compared with the 
more mature one. Is this difference to be ascribed to a specif- 
ically higher percentage utilization on the part of the younger 
animal, or is it due to a relatively greater consumption of feed 
or the relatively high net energy values which usually char- 
acterize the feeds given the young animal, particularly milk? 
The mere fact, for example, that a young animal consuming 
milk utilized a higher percentage of the feed energy than did 
the same animal later upon a mixed ration would not necessarily 
show any physiological superiority on the part of the younger 
animal but might be due solely to the difference in the kind 
of feed consumed. So, too, the mere ability to consume 
relatively large amounts of highly concentrated feed in the 
form of milk and thus to secure a large surplus above the 
maintenance requirement might (360, 510) give the younger 
animal a marked economic advantage without indicating any 
more efficient conversion of the surplus energy supplied than 
in the older animal. 

Unfortunately, investigations regarding the utilization of 
feed at different ages have been few in number and the avail- 
able data regarding net energy values for growth are exceed- 
ingly meager. To a large extent it is necessary to be content 
with comparisons of a very general nature, leading to proba- 
bilities only. 

473. Experiments on suckling animals. — The experiments 
by Soxhlet on calves and those by Wilson on pigs cited on 
previous pages (458) and likewise an investigation by Rubner 
and Haubner 1 on infants afford some data for approximate 
estimates of the percentage of the metabolizable energy of milk 
utilized by growing animals. 

The computations involve a number of uncertain assump- 
tions, particularly as regards the maintenance requirement, 
and none of them afford a satisfactory basis for comparing 
the utilization of the metabolizable energy of milk at different 
ages. It is of some interest, however, to compare the average 
utilization computed from these experiments with that esti- 
mated by the use of Rubner's factors for the " specific 
dynamic action " of equal amounts of pure nutrients on mature 
animals. 

1 Ztschr. Biol., 36 (1898), 1 ; 38 (1899), 315. 



392 



NUTRITION OF FARM ANIMALS 



As explained in Chapters VIII and XVII (366, 759), Rubner's 
"specific dynamic action" is synonymous with the energy expendi- 
ture caused by the consumption of feed, and if it be subtracted from 
the metabolizable energy the remainder is the net energy. The per- 
centage utilization is of course the net energy divided by the metab- 
olizable energy. 

Estimated in this way, the percentage utilization would be 
as shown in the first column of the following table, the second 
and third columns of which show the utilization as computed 
by the writer both with and without a io per cent addition to 
the fasting katabolism as estimated from the data on mature 
animals. 

Table 89. — Estimated Utilization of Metabolizable Energy of 

Milk 



Rubner's experiments 
Soxhlet's experiments 
Wilson's experiments 



Computed, 
Using 

Rubner's 
Factors 



% 
84.08 
86.18 
83-99 



Computed by Writer 



Fasting 

Katabolism 

Same as in 

Mature 

Animals 



% 
73.10 

73-77 
70.31 



Fasting 
Katabolism 
10% 
Greater 
than in 
Mature 
Animals 






% 

75-56 

75-47 



While it is clear that no final conclusions can be based upon 
small differences between figures obtained as these have been, 
it seems suggestive, nevertheless, that the actual experiments 
with growing animals show a lower average utilization than 
would be expected from Rubner's results upon mature animals. 
Moreover, Wilson's results are apparently lower than those 
which may be computed from Meissl's and Kornauth and 
Arche's respiration experiments upon mature swine consuming 
grain (757). Certainly these comparisons afford little sup- 
port ttf the notion that the utilization of energy in the physio- 
logical sense by young animals is much higher than that by 
mature animals. 



GROWTH 393 

474. Experiments on older animals. — Of experiments upon 
older animals those of Kern and Wattenberg on lambs and of 
Tschirwinsky on pigs (458), permit an approximate computa- 
tion of the utilization of the feed energy during growth and 
afford data for some comparisons, although in neither case 
were very young animals employed, the lambs being between 
6 and 7 months old at the beginning of the experiment and the 
pigs between 9 and 10 weeks. 

On the whole, the results of these experiments seem to indi- 
cate, if anything, a rather lower percentage utilization by the 
younger animals as compared with the older. At any rate they 
fail to show any superiority on the part of the former. The same 
is true of the results of experiments by Armsby and Fries l upon 
steers 10 to 27 months old in which the availability was deter- 
mined by the use of the respiration calorimeter. While not de- 
cisive, the results seem to indicate a slightly lower availability of 
the mixed grain and possibly of the hay for the younger animals. 

475. Embryonic growth. — Several experimenters, especially 
Tangl and his associates 2 and Bohr and Hasselbalch, 3 have 
determined the energy expended in the development of the 
embryo in oviparous animals, i.e., in the organization of the 
substances of the egg into embryonic tissue. These investi- 
gations have shown that a relatively large proportion of the 
chemical energy contained in the egg is evolved as heat during 
the process of development, so that the percentage recovered 
in the embryo, ranging from 60 to 68 per cent, is distinctly 
lower than the utilization of the energy of milk by suckling 
animals as computed in a previous paragraph (473). More- 
over, they show that the utilization of the energy of the egg is 
notably less in the earlier than in the later stages of incubation, 
as low a figure as 28 per cent having been observed after 10 
days' incubation. 

The method may be illustrated by the results of two experiments 
by Tangl and Mituch, each upon three hens' eggs. From analyses of 
similar eggs from the same hen, it was computed that the three used 
contained respectively 229.72 Cals. and 291.38 Cals. chemical energy. 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128 (1911), 51. 

2 Arch. Physiol. (Pfliiger), 93 (1903), 327; 98 (1903), 490; 104 (1904), 624; 121 
(1908), 423 and 437. 

3 Skand. Arch. Physiol., 10 (1900), 149 and 353 ; 14 (1903), 398. 



394 



NUTRITION OF FARM ANIMALS 



At the end of incubation the embryo 1 was separated from the yolk 
sack and its contents and the energy of each determined with the fol- 
lowing results : — 

Table 90. — Utilization of Energy in Incubation 



Original energy of eggs 

Remaining in yolk sack and contents 

Used for production of embryo . . 

Recovered in embryo 

Percentage recovered 



Eggs from 
Hen VIII 



229.72 Cals. 

63-95 Cals. 
165.77 Cals. 

99.24 Cals. 

59.87 Cals. 



Eggs from 
Hen X 



291.38 Cals. 
94.64 Cals. 

196.74 Cals. 
125.66 Cals. 
63.84 Cals. 



In other words, 35 to 40 per cent of the energy of the egg substance 
used was not recovered but escaped as heat. Comparison with the 
loss of dry matter showed that the material thus katabolized consisted 
substantially of fat. No loss of nitrogen was observed. 

Experiments on mammalian and reptilian embryos, especially 
by Bohr, 2 by Murlin 3 and by Carpenter and Murlin, 4 appear in 
accord with the foregoing conclusion, since they show that the 
metabolism of the embryo per unit of weight is as great or 
greater than that of the mature animal, despite the fact that the 
maintenance requirement of the former must be decidedly less. 

The growth of the embryo consists essentially of the organ- 
ization of protein tissue. The fact that there is no loss of nitro- 
gen during incubation would indicate that chemically the 
process is effected by a cleavage and resynthesis of protein 
which appears to be a nearly isothermic process (233, 367 d). 
Apparently the organization of the protein into structure is 
what calls for the large expenditure of energy. 

476. Summary. — The experimental results mentioned in the 
foregoing paragraphs may be briefly summarized in the follow- 
ing statements : — 

In the case of suckling animals, while no direct comparisons 
of the same animal at different ages are available, the utilization 
of the metabolizable energy of milk for growth appears to be 

1 Including the egg membranes. 

2 Skand. Arch. Physiol., 10 (1900), 413; 15 (1904), 23. 

3 Amer. Jour. Physiol., 26 (1910), 134. 4 Arch. Inter. Med., 7 (1911), 184. 



GROWTH 395 

distinctly less than would be expected from Rubner's results 
on the utilization of pure nutrients by mature animals. In the 
case of swine, moreover, the utilization appears to be even less 
than that of the metabolizable energy of grain by mature ani- 
mals, although the contrary would naturally have been antici- 
pated. The results with older animals, while far from conclusive, 
seem, if anything, to indicate a lower utilization by younger 
animals as compared with older ones and at any rate fail to 
show that it is any greater in the former case. 

The results on embryonic growth show a relatively large 
expenditure of energy in development and indicate a compara- 
tively low utilization of energy. This large expenditure of 
energy in development seems to be required chiefly for the 
organization, in the broader sense, of the embryonic structure 
rather than for the mere chemical transformation of egg sub- 
stances, and it seems to be relatively greater in the young as 
compared with the more mature embryo. 

477. Provisional hypothesis. — While it would be rash to 
draw any final conclusions from the foregoing data, it may be 
permissible to formulate a working hypothesis to the effect 
that the conversion of feed protein (including the protein of 
the egg) into tissue requires a considerably greater relative 
expenditure of energy than does the conversion of surplus feed 
into fat, the difference representing what might be called the 
work of organization, i.e., the formation of organized structure 
in the young animal and especially in the embryo. It has 
been shown (463) that the rate of growth decreases rapidly 
with increasing age. Accordingly, the work of organizing new 
protein tissue, so far as this is measured by the storage of pro- 
tein, must constitute a steadily diminishing proportion of the 
total energy expenditure of the organism, since as the animal 
grows older the increase consists to a diminishing extent of 
protein and to an increasing extent of fat. The percentage 
utilization of the feed energy would therefore, upon this hypothe- 
sis, tend to increase. It would be least immediately after birth 
and after two to four months would become relatively small, 
corresponding to the changing character of the gain. Probably 
by the time an animal has been weaned and is consuming the 
normal feed of its species, the percentage utilization of the feed 
energy might be assumed to be not much less than that ex- 



396 NUTRITION OF FARM ANIMALS 

hibited by the mature animal and at any rate to be practically 
proportional to it. This would mean, of course, that the net 
energy values of feeding stuffs for maintenance and fattening 
might be used also to measure at least their relative if not their 
absolute net energy values for growing animals. 

The determination of the validity of this provisional con- 
clusion offers an interesting and profitable field for investigation. 

§ 3. The Feed Requirements for Growth 

478. Contrast with fattening. — In the case of fattening 
animals the conception of the feed requirement, particularly as 
regards energy, is somewhat artificial, since the extent of the 
fattening depends, within the limits of the animal's capacity, 
largely upon the amount of feed supplied. Growth, on the 
other hand, unless the feed fails to supply the necessary materials 
and thus becomes a limiting factor, goes on at a rate substan- 
tially determined by other conditions, the most obvious of 
which are the species, individuality and age of the animal. 
Indeed, it may be said that, within normal limits, the capacity 
for growth determines the feed consumption rather than the 
reverse. Heavy feeding may cause fattening but it does not 
appear, at least in the case of the higher animals, to materially 
accelerate growth, although Eckles * observed the growth of 
dairy calves to be somewhat more rapid upon heavy as com- 
pared with scant rations. In growth, therefore, as in mainte- 
nance, there is a real requirement to be satisfied, its measure be- 
ing the amount and character of the increase which the young 
animal is capable of making under normal conditions. 

Mention has been made (372) of the interesting results of experi- 
ments by Waters 2 upon growth under adverse conditions, while 
Osborne and Mendel 3 have shown that growth which has been sus- 
pended for a time because of inadequate feed supply may be resumed 
when this deficiency is made good (deferred growth). Neither of 
these possibilities, however, invalidates the statement just made that 
the continued maintenance of a normal rate of growth requires a 
definite supply of matter and energy. 

1 Mo. Expt. Sta., Bui. 135, 1915. 

2 Soc. Prom. Agr. Science, Proc. 29th Annual Meeting, 1908, p. 71. 

3 Jour. Biol. Chem., 18 (1914), 195; 23 (1915), 439; Amer. Jour. Physiol., 40 
(1916), 16. 



GROWTH 



397 



479. Total increase in normal growth at different ages. — 

The feed requirements of the growing animal as regards protein 
and energy depend in the first place on the amounts which such 
an animal is capable of storing up in normal growth. From the 
data regarding the rate of growth recorded in § i of this chapter, 
even though they are somewhat fragmentary, it seems possible to 
derive average figures regarding the storage of protein and energy 
in growth at different ages which may be of some value as a guide 
in estimating the feed requirements of the growing animal. 

As regards protein, it was shown that the rate of gam per 
iooo live weight apparently does not vary widely as between 
cattle, sheep and swine, and an empirical formula (463) was 
given by which its amount at any age may be approximately 
estimated. As regards energy, fewer data are available, es- 
pecially for farm animals, but the graphic representation in Fig. 
39 of the results recorded in Table 8i (464) shows a diminish- 
ing rate of gain of energy as the animal grows older. 

In the following tabulation the daily gain of protein at differ- 
ent ages has been calculated by means of the formula just men- 
tioned and the gain of energy estimated from the smoothed graph 
of Fig. 39. The two together may be taken as an approximate 
expression of the normal increase in growth at different ages. 

Table 91. — Daily Increase in Growth per iooo Pounds Live Weight 



Age 



io days 

20 days 

30 days 

60 days 

90 days 

120 days 

150 days 

180 days 

210 days 

240 days 

270 days 

300 days 

1 year 

1 I years 

2\ years 



Protein 



Pounds 
4-50 
3-38 
2.70 
I.50 
I.23 
O.96 
0.79 
O.68 

0.59 
0.52 

o.47 
0.42 

0.35 
O.24 

O.I5 



Energy 



Therms 

24-5 
21.8 
20.0 
16.O 
13.O 

n-5 
10.0 
9.0 
8-5 
7-5 
7.0 

6-5 
5-5 
4.0 

2-5 



39§ 



NUTRITION OF FARM ANIMALS 





























































& 






% 

3 

i 
5 










a 






"a 

5 


• *> 

2 £ 










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Therms per iooo 
pounds live weight 



GROWTH 399 

Energy requirements 

480. Computation from daily increase. — The estimates 
contained in the foregoing table of the amount of energy 
stored up in growth, although unfortunately based on scanty 
data, show, to the extent to which they can be relied on, 
the amounts of net energy which are necessary for the 
support of growth without any considerable fattening. 
Since the results described in § 2 render it probable that 
the net energy values of feeding stuffs for growth do not 
differ widely from those for maintenance or for fattening (477), 
the figures of the table, with the addition of the maintenance 
requirement, would afford a basis for computing rations for 
young animals. 

481. Computation from gain in live weight. — Another 
method of computation furnishes to a certain degree a check 
upon the results recorded in the last table. The amount of 
energy stored up in the increase at different ages may be esti- 
mated by applying the results regarding the energy values per 
unit of increase which are recorded in Table 79 (458) to the gain 
of live weight actually observed in the growth of animals under 
normal conditions. 

a. Cattle. — From data secured at the Missouri Experiment 
Station 1 regarding the rate of growth of 5 Hereford, 6 Jersey, 
2 Ayreshire and 5 Holstein calves, the writer has computed 
the following figures for the daily gain of energy per 1000 pounds 
live weight by calves. 

For an animal one month old, it is assumed that the energy con- 
tent of the increase in live weight was the same as the average of 
Soxhlet's respiration experiments, viz., 11 70 Cals. per pound, and 
that this increased at a uniform rate to a maximum of 3000 Cals. per 
pound at 18 months old. The observed daily gain of energy has been 
computed per 1000 pounds live weight to eliminate the influence 
of the varying size of the different breeds. The average daily gains 
per 1000 pounds live weight are computed for each breed separately, 
and these means are again averaged, i.e., each breed has been 
given equal weight. None of the animals were fattened to any great 
extent. 

1 Private communications from Professors P. F. Trowbridge and C. H Eckles. 
Data for the dairy breeds have been published in Bui. 135 of the Missouri Station. 



400 



NUTRITION OF FARM ANIMALS 



Table 92. — Average Gains by Growing Calves per iooo Pounds 

Live Weight 



Approximate Age 


Daily Gain in Live 
Weight 


Estimated Energy 

Content of i Lb. 

of Increase 


Daily Gain or 
Energy 


Months 


Pounds 


Therms 


Therms 


0-1 


12.73 


1. 1 70 


14.89 


o-i 1 


19-54 


1. 1 70 


22.86 


1-2 


10.69 


I.272 


13.60 


2-3 


7.32 


1-374 


IO.06 


3-4 


7.84 


I.476 


n-57 


4-5 


5-29 


1.578 


8-35 


5-6 


4-53 


I.680 


7.61 


6-7 


2.05 


I.782 


3-65 


7-8 


1.99 


I.884 


3-75 


8-9 


1.94 


I.986 


3-85 


9-10 


2.68 


2.088 


5.60 


10-11 


2-57 


2.190 


5-63 


11-12 


1.58 


2.292 


3.62 


12-18 


1.64 


2.904 


4.76 


18-24 


1.25 


3.000 


3-75 



b. Swine. — Similar approximate estimates may be made for 
the pig from data reported by Henry. 2 At weekly intervals, 
up to 70 days old, the computation is based on the live weights 
and gains shown in Henry's table. The gains by the older 
animals are estimated on the basis of his statement 3 that the 
larger breeds should weigh 250 pounds at one year, it being 
assumed that the rate of gain would decrease at an approxi- 
mately uniform rate. 

It is evident that the results on the heavier animals as compiled 
by Henry were obtained by heavy feeding for fattening, since it may 
be computed from the figures for the weights and gains that the ani- 
mals would reach a weight of about 320 pounds at about 10 months 
old. The energy content per pound of gain is estimated on the as- 
sumption that it would increase uniformly from the average of 
about 500 Cals. obtained by Wilson and by Wellmann for young 
pigs (458) up to 2485 Cals. as computed in Table 65 of Chapter X 
(442) for Soxhlet's swine No. 3 at 500 days old. 



1 Average of Soxhlet's experiments. 
3 Loc. cit., p. 553. 



Feeds and Feeding, 10th Ed., p. 499. 



GROWTH 



401 



Table 93. — Average Gains by Growing Pigs per iooo Pounds Live 

Weight 



Approximate Age 


Daily Gain est Live 
Weight 


Estimated Energy 

Content of i Lb. 

of Increase 


Daily Gain of 
Energy 


Days 


Pounds 


Therms 


Therms 


* 0-7 


78.55 


532 


41.79 


7-14 


65.09 


559 


36.38 


14-21 


47.62 


585 


27.86 


21-28 


34.62 


6l2 


21.19 


28-35 


31-53 


639 


20.15 


35-42 


25.09 


665 


16.69 


42-49 


27.72 


693 


19.21 


49-56 


29.48 


720 


21.23 


56-63 


24.92 


750. 


18.69 


63-70 


21-54 


776 


16.71 


70-90 


14.92 


827 


♦ 12.34 


90-120 


n-45 


945 


10.82 


120-150 


8-43 


1063 


8.96 


150-180 


6.79 


1181 


8.02 


180-210 


5-68 


1300 


7.38 


210-240 


4.87 


1418 


6.91 


240-270 


4.26 


1536 


6-54 


270-300 


3.78 


1654 


6.25 


300-330 


3 -40 


1772 


6.03 


330-360 


3-o8 


1891 


5.82 



482. Estimated averages. — The foregoing results have 
been plotted in Fig. 39 (479) for comparison with those 
derived from the computations of § 1, regarding the rate of 
storage of energy. By drawing smooth curves through the 
results for calves and for pigs, respectively, the following 
approximate estimates of the average rate of gain of energy 
by these two species have been obtained. No similar data 
appear to be available for other species of farm animals. 
The graph would seem to indicate that the results for cattle 
may apply fairly well also to sheep, although no figures for the 
latter species are recorded below 300 days old. Preliminary 
computations on the basis of the live weights assumed by 
Kellner for lambs at different ages seem to indicate higher 
figures for the first six months, especially for animals of the 
mutton breeds. 



2 D 



402 



NUTRITION OF FARM ANIMALS 



Table 94. — Estimated Rate of Gain of Energy per Day and iooo 

Pounds Live Weight 



Age 



30 days . , 

60 days . , 

90 days . . . 

120 days . . 

150 days . , 

180 days . , 

210 days . . 

270 days . . 

365 days . . 

18 months 

24 months . 

30 months 



Cattle 
(and 

Sheep?) 



Therms 

18.O 

13-5 

11.0 

9.0 

7-5 
6.0 

5-25 
5.o 

4-75 
4-5 
4-25 
4.0 



Swine 



Therms 

20.0 

14-5 
II.O 

9.0 

8.8 

7-5 
7.0 

6-5 
6.0 



It cannot be claimed that the foregoing computations are 
particularly satisfactory. The data are scanty, and the ele- 
ment of personal judgment unavoidably enters, especially into 
the estimates of the energy value of a unit of increase in live 
weight. Nevertheless, while there are very considerable 
divergencies at certain points, there is after all a certain general 
agreement in the results, and they may perhaps serve as a first 
approximation towards an expression of the growth capacity 
of farm animals in terms of energy storage. It is much to be 
regretted that such a fundamental factor in determining the 
feed requirements for growing animals is so imperfectly known 
and the determination of the amount and composition of the 
increase in growth at different ages, whether by means of com- 
parative slaughter tests or with the aid of respiration or calori- 
metric experiments, offers an interesting field for investigation. 
With the smaller animals, such as pigs, lambs and particularly 
fowls, it would appear that such determinations might be made 
without great difficulty. 

483. Total energy requirements. — The foregoing figures 
attempt to show approximately the actual storage of energy 
per 1000 pounds of live weight by growing animals at various 
ages. An adequate ration for such an animal, however, must 



GROWTH 403 

not only supply net energy equal to that contained in the growth 
made, as indicated by the foregoing table, but in addition 
sufficient net energy for maintenance, the sum of the two being 
the total net energy required by the animal. Computing 
from Table 94 and from the estimated live weight at different 
ages x the energy storage per head and adding the maintenance 
requirement computed in proportion to the two-thirds power 
of the live weight (347) gives the total energy requirements 
shown by Table IV b of the Appendix. 

Protein requirements 

484. Minimum requirement. — As with the energy of the 
feed, the protein supply of the growing animal is essentially a 
limiting factor. A deficient supply or one lacking certain 
essential " building stones" (465), may check growth tem- 
porarily or permanently through simple lack of material, but 
it does not appear that a surplus of protein can materially 
stimulate the rate of growth. 

Granting the approximate accuracy of the estimates of the 
actual gain of protein in normal growth made on previous 
pages (463, 479), the quantity of digestible feed protein re- 
quired in the ration of the growing animal at any particular 
age will depend upon what proportion of the latter can be con- 
verted into body protein and stored up, i.e., upon the percentage 
utilization of the feed protein (470). As was shown in the 
preceding section, however, this is very imperfectly known. 
If, on the basis of Fingerling's and Just's results (471), it be 
assumed that the utilization may approach 100 per cent, then 
the amounts estimated in Table 91 (479), with the addition of 
about 0.5 per 1000 for maintenance, would be the least amounts 
of digestible protein which must be supplied to support the 
normal increase of protein tissue. 

485. Results in practice. — As a matter of fact, however, 
experience seems to show that a more liberal supply of feed 
protein than is indicated by these estimates is at least advan- 
tageous if not necessary in the actual rearing of animals. While 
there are few investigations on record directed specifically to 
the determination of the minimum protein requirements of 
1 In direct proportion to the live weight. 



404 



NUTRITION OF FARM ANIMALS 



growing animals, there are a considerable number of experi- 
ments, especially upon immature fattening animals, in which 
the increase of live weight has been determined upon rations 
otherwise reasonably similar but containing varying propor- 
tions of protein. 

In the immature fattening animal, it seems safe to assume that the 
feed protein (in excess of maintenance) is applied substantially to the 
support of growth and that this growth goes on parallel with the 
fattening process but more or less independent of it. There appears 
to be no evidence that protein specifically stimulates or aids fatten- 
ing, so that conclusions regarding the protein supply drawn from 
fattening experiments may be regarded as applicable to growth without 
fattening. 

If in such an experiment, in which the total amounts of feed 
consumed do not differ widely, it appears that the smaller 
amount of protein has been as efficient as the larger as regards 
gain in live weight, and if the gain appears to be normal in 
amount, there is a strong presumption that the lesser amount 
of protein was at least sufficient for the needs of the animal for 
growth and maintenance, while if a block test shows a normal 
character of increase this presumption is further strengthened. 
Obviously, results of this sort cannot be relied on to fix definitely 
the lower limit of protein supply, but they may furnish indica- 
tions regarding it. 

486. Experiments with cattle. — In the experiments upon 
calves by Soxhlet, De Vries Jzn and Neumann, included in 
Table 80 (463), showing the rate of gain of protein, the amounts 
of digestible protein consumed as compared with the actual 
gains were as follows : — 

Table 95. — Protein Consumed by Calves 





Feed 


Age 


Per 1 000 Live Weight 




Digestible 
Protein 


Gain of 
Protein 


Soxhlet 

De Vries Jzn .... 

Neumann 

De Vries Jzn .... 
De Vries Jzn .... 


Whole milk 
Skim milk 
Skim milk 
Skim milk 
Skim milk 


19 

40 

55 

65 

100 


4.90 
4.67 

5-72 

3-99 
3-32 


3.22 
2.19 
2.22 
I.36 
1. 19 



GROWTH 



405 



In the light of Fingerling's results upon suckling calves 
(466), however, there can be little doubt that the protein supply 
in these experiments was unnecessarily great, especially with 
the older animals. 

The writer * has elsewhere discussed some of the earlier live 
weight results bearing upon the protein supply of immature 
fattening cattle which seem to indicate much higher require- 
ments than might be deduced from the actual gains of protein 
at the several ages. Those results are here tabulated in a 
slightly altered form and with the addition of a subsequent 
experiment by Schneidewind. 2 The summary of course repre- 
sents to a degree the judgment of the writer and the figures are 
to be interpreted as indications rather than as determinations. 



Table 96. — Estimated Protein Requirements of Cattle 



Age 
Years 


Experimenter 


Digestible Protein per 
1000 Live Weight 


1 


Waters 


2.00 


if 


Jordan 


1.63 


i| 


Schneidewind 


2.00 


2 


Schneidewind 


1.60 


2 


Jordan 


1.50 


2 


Frear 


1.50 


2 


Waters 


1.50 to 2.00 


2-2^ 


Schneidewind 


1.67 


a* 


Mumford 


1.50 to 2.00 


3 


Frear 


1. 00 


3 


Jordan 


1.26 



The foregoing estimates correspond in general with the pro- 
tein requirements for growing cattle as formulated in the WolfT- 
Lehmann and Kellner feeding standards (790-793) . In experi- 
ments upon two steers, directed principally to other questions, 
Armsby and Fries 3 observed a normal rate of increase in weight 
upon rations containing amounts of digestible protein much 
smaller than are called for by current feeding standards, although 
still in excess of the estimated normal gain of protein for the cor- 

1 U. S. Dept. of Agr., Bur. Anim. Indus., Bui. 108 (1908), pp. 60—65. 

2 Landw. Jahrb., 36 (1907), 687. 

3 U. S. Dept. of Agr., Bur. Anim. Indus., Bui. 128 (1911), pp. 88-90. 



406 



NUTRITION OF FARM ANIMALS 



responding ages. The experiments do not show, however, that 
these amounts might not have been still further reduced. 

Table 97. — Digestible Protein per iooo Pounds Live Weight. — 

Armsby and Fries 



Steer A 


Steer B 


Approximate Age 


Digestible Protein 


Approximate Age 


Digestible Protein 


Months 


Pounds 


Months 


Pounds 


9h 


I.42 


12 


I.64 


12! 


I.40 


I4l 


I.77 


18 


I.09 


19 


I.25 


2o| 


I.03 


22 


I.23 


25^ 


O.72 


27 


0.85 



Henry and Morrison x likewise report the results of unpub- 
lished experiments by Haecker in which growing fattening 
steers made satisfactory gains on amounts of digestible protein 
intermediate between those recommended by Kellner for beef 
and for dairy breeds. 

On the other hand, Fingerling's investigations on calves 
4^-11 months old, already cited in a discussion of the utiliza- 
tion of feed protein (471), indicate that a much lower level of 
protein supply may be adequate to support normal growth. 

The experiments 2 were made upon four grade or full-blood Sim- 
menthaler calves from four to seven months old at the beginning of 
the trials, and belonging to early-maturing strains. The rations fed 
consisted of a basis of hay or straw, or both, to which were added in 
varying proportions wheat gluten, peanut oil and starch with the 
necessary amount of salt. The protein supply was varied by varying 
the amount of wheat gluten, the energy values of the rations being 
kept as nearly identical as possible by corresponding changes in the 
starch and oil. The experiments were intended to test the necessity 
for the relatively large amounts of protein called for by the current 
standards and also the influence of a deficient energy supply upon the 
gain of protein. 

As appears from Table 87, the medium rations, supplying in 
the neighborhood of 1.2 pounds of protein per 1000 pounds 
live weight, were clearly sufficient to meet the demands of 
the maximum possible protein gain, since an increase of the 

1 Feeds and Feeding, 15th Ed., p. 670. 2 Landw. Vers. Stat., 76 (191 2), 1. 



GROWTH 



407 



digestible protein to more than double that amount failed to 
produce any greater gain but simply increased the protein 
katabolism. That such was the case is likewise indicated by 
the fact that the actual gains of protein per 1000 live weight 
in these cases agree very well with those computed by the use of 
the formula on page 378, tending to be greater rather than less. 1 
487. Experiments with sheep. — The amounts of digestible 
protein necessary for growing sheep as formulated by Wolff in 
his original feeding standards were based upon experiments of 
his own 2 in which the digestibility of the feed and the gain in 
live weight were determined. Later Weiske 3 made a series 
of ten determinations of the nitrogen balance of two lambs at 
ages ranging from four to twenty-four months. The rations 
consumed were meadow hay with a decreasing proportion of 
grain (peas) in Periods I to VII and of hay alone in the re- 
maining periods, and the rate of increase in live weight was 
somewhat greater than that of similar animals on pasture. The 
following table contains the results of both investigations. 

Table 98. — Protein Consumed by Grow:tng Sheep 



Age 


Digestible Protein 
per 1000 Pounds 
Live Weight 


Experimenter 


7 to 9 months 

8 to 9 months 

12 to 14 months 

24 months 


Pounds 
3-76 
3.26 
3.16 
2.78 
2.96 
2.76 
1.87 4 
2.38 
2.30 
1.38 4 
2.16 
1.96 
1.61 
I.92 
1.22 


Weiske 

Weiske 

Wolff 

Weiske 

Wolff 

Weiske 

Wolff 

Weiske 

Weiske 

Wolff 

Weiske 

Weiske 

Wolff 

Weiske 

Weiske 



1 The one exception to the above statement is the case animal G in Period III, 
in which the energy content of the ration was somewhat low. 

2 Landw. Jahrb., 2 (1873), 221. 3 Ibid., 9 (1880), 205. 

4 Believed by Wolff to be too low. 



4o8 



NUTRITION OF FARM ANIMALS 



Bull and Emmett 1 have compiled the results of fifty American 
experiments on fattening lambs, comprising 5127 animals, 
and computed the protein and net energy content of the rations 
consumed. They divide the animals into four classes accord- 
ing to the live weight, and subdivide these classes into groups 
according to the amount of digestible protein consumed. A 
comparison of these groups shows in general that in each class, 
even with a liberal supply of feed energy, the rate of growth 
increased as the supply of protein increased up to a certain 
fairly well-defined amount, beyond which a further increase 
of protein had in general little or no effect. The authors es- 
timate the amounts of digestible protein necessary to ensure 
satisfactory gains by fattening lambs as follows : — 

Table 99. — Estimated Protein Requirements of Fattening Lambs 



Live Weights 


Estimated Age 


Digestible Protein per 
1000 Lb. Live Weight 


Pounds 
50-70 
70-90 
90-110 
110-150 


Months 

5 

7 

9 

15 


Pounds 

3-1-3-3 
2.5-2.8 
2.2-2.4 
1. 4-1. 9 



On the other hand, Just's results on lambs recorded in Table 
88 (471), like those of Fingerling in calves, point to a much 
lower protein requirement. 

488. Experiments with swine. — As is illustrated in Table 
93 (481 b), the swine is distinguished above other farm quad- 
rupeds by its very rapid growth, especially in the earlier stages. 
The young pig is able to double his weight in little more than 
a week and to nearly treble it in two weeks, a rate of growth 
reached or exceeded by no farm animal with the possible ex- 
ception of young fowls. 

Such a rapid rate of growth implies, of course, a correspond- 
ingly large storage of protein, a conclusion fully confirmed by 
the investigations of Ostertag and Zuntz, of Wilson, and of 
Sanford and Lusk, cited in § 1 (463) which showed an average 

1 Ills. Expt. Sta., Bui. 166 (1914). 



GROWTH 409 

daily gain of from six to nine pounds of protein per thousand 
live weight during the first sixteen days after birth. Plainly, 
young pigs need a relatively large supply of protein in their feed, 
but unfortunately no attempts have thus far been reported to 
determine the minimum of feed protein necessary at different 
ages and especially by older pigs, simply to ensure normal 
growth. There are on record, however, a considerable number 
of experiments in which rations supplying varying amounts of 
protein have been fed to fattening pigs and the effects upon the 
make-up of the carcass and upon the rate of increase in live weight 
observed. These experiments have served to demonstrate in a 
striking manner the practical advantages of a liberal protein 
supply and while in many instances the minimum protein re- 
quirement may have been considerably exceeded, nevertheless, 
the results as a whole are perhaps no less useful as a guide in 
practice. 

It is impossible to include here even an enumeration of the large 
number of experiments of this sort. For a summary of earlier inves- 
tigations the student may be referred to the summary published by 
Wolff in 1876. l A considerable number of earlier experiments in the 
United States as compiled by the writer gave results of the same 
general nature. 

The later experiments upon this subject may be divided into those 
directed more specifically to the determination of the influence upon 
quality and chemical composition of the carcass and those in which 
the increase in live weight was the principal criterion. 

489. Effect of insufficient protein upon the carcass of pigs. — 

Striking results as to the make-up of the carcass in young pigs 
have been reported by several investigators in experiments in 
which exclusive maize feeding was compared with the use of 
mixed rations supplying much more protein and ash. The 
trials have been popularly spoken of as " Feeding for fat and 
for lean." In reality they are a study of the effect of inade- 
quate protein (and ash?) supply in limiting growth. The 
subject was first taken up by Sanborn 2 and soon after by 
Henry. 3 In general it was found that in the pigs receiving the 

1 Ernahrung der landwirtschaftlichen Nutztiere, pp. 465-496. 

2 Mo. Agr'l College, Bui. 10, 14 and 19. 

3 Wis. Expt. Sta., Rpts 4, 5, 6, 17, 18, 19 and 21. 



410 NUTRITION OF FARM ANIMALS 

low protein (maize) rations the weights of blood, of internal 
organs and in some cases of certain individual muscles were 
relatively less than with comparable animals receiving the 
high protein (mixed) rations, while on the other hand, the 
deposits of adipose tissue appeared notably greater in the maize- 
fed animals. 

Since these investigations were made it has become a well-recog- 
nized fact that the mixed proteins of maize are inadequate to sup- 
port rapid growth (783) and the results reached are to be regarded 
as being to a considerable degree the expression of this qualitative 
deficiency. 

As regards the quantitative aspect of the experiments it is to be 
remarked that in most instances the difference between the rations 
as regards protein was purposely made large. While the experiments 
have made it clear that exclusive maize feeding fails to afford an ade- 
quate supply of protein for growing pigs, it does not follow that as 
large quantities of protein as were contained in the contrasting rations 
were necessary. In the later Wisconsin experiments especially, as 
the writer has pointed out, 1 the gain in live weight was often little 
greater on the high protein than on the low protein rations and some- 
times even less. 

Furthermore, while the animals were compared more or less ex- 
tensively as to the weights of the various organs at the close of the 
feeding, and in one instance at least the carcasses were analyzed, the 
experiments were not of the nature of comparative slaughter tests 
and did not afford data for computing the actual amount of protein 
gained. Moreover, the results upon the carcasses analyzed 2 seem to 
indicate that the rations affected the adipose tissue as to its distribu- 
tion through the carcass rather than as to its total amount. 

Finally, the striking results as to general thrift, and especially as 
to the growth and strength of the bones, are probably to be attributed 
to differences in the ash supply (496) , quite as much as to differences 
in the protein supply. 

On the whole, while these investigations are valuable from 
the standpoint of practice as a demonstration of the ill effects 
of a deficient amount or quality of protein, it cannot be said 
that this class of experiments affords very definite information 
as to the actual protein requirements of pigs. 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), p. 74. 

2 Iowa Expt. Sta., Bui. 48 (1900), pp. 373-451; U. S. Dept. Agr., Bur. Anim. 
Indus., Bui. 108, p. 75,. 



• GROWTH 411 

490. Fattening experiments with pigs. — Of the more recent 
experiments upon the influence of the protein supply upon the 
rate of gain of immature fattening pigs, four series made by the 
Halle Experiment Station at Lauchstadt l and a series of co- 
operative experiments at a number of the German experiment 
stations under Kellner's general direction are of special interest. 
While these relate primarily to fattening, the comparative 
results with rations of equal energy content should furnish 
some indications as to the sufficiency of the protein supply, 
since the rate of increase of protein tissue can hardly be sup- 
posed to differ materially from that in simple growth without 
fattening. 

In the Halle experiments it is interesting to note the gradual 
lowering of the average protein supply from the high level of 
the first series. The final series seems to show that satis- 
factory results may be obtained from rations whose protein 
content per 1000 pounds at the different weights of the animal 
is as follows, although the earlier trials seem to indicate some- 
what higher figures. 

Table 100. — Estimated Protein Requirements of Fattening Pigs 

At weight 77-100 lb 4.0 lb. 

At weight 1 10-165 lb 3.0 lb. 

At weight 165-220 lb 2.0-2.5 lb. 

At weight over 220 lb 2.0 lb. 

In 1906 cooperative experiments were initiated by the Ger- 
man Agricultural Council at a number of German experiment 
stations upon 'the value of potatoes as feed for fattening pigs 
and especially upon the protein supply necessary for their 
most complete utilization. The results of experiments upon 
this point at eleven stations, upon a total of 184 animals, have 
been discussed by Kellner 2 under whose general direction the 
work was done. According to Kellner 3 young fattening pigs 
should receive per 1000 live weight the following amounts 
of protein : — 

1 Landw. Jahrb., 28 (1899), 947 ; 31 (1902), 916 ; 36 (1907), 679 ; 39, Ergzbd. Ill 
(1910), 179. 

2 Ber. Deut. Landw. Rat, Heft 3 (1908). 

3 Die Ernahrung der landw. Nutztiere, 5th Ed., p. 488. 



412 NUTRITION OF FARM ANIMALS 

Table ioi. — Kellner's Standards for Fattening Pigs 



Age 


Average Live Weight 


Digestible Protein per 
1000 


Months 


Kgs. 




2-3 


20 


6.2 


3-5 


50 . 


4-5 


5-6 


65 


3-5 


6-8 


90 


3-o 


9-12 


130 


2.4 



The outcome of the cooperative experiments tended to con- 
firm these standards, indicating that any considerable departure 
from them will fail to meet the requirements of rapid growth in 
the best strains of animals or to secure the largest returns. 
On the other hand, the fourth Lauchstadt series perhaps points 
in the direction of lower standards, especially for the more 
mature animals. For breeding animals Kellner recommends 
somewhat smaller amounts of protein, viz. : — 

Table 102. — Kellner's Standards for Growth of Pigs 



Age 


Live Weight 


Protein per 
1000 


Months 

2-3 
3-5 
5-6 
6-9 
9-12 


Kgs. 

20 
40 

55 

80 

120 


6.2 
4.0 

3-o 

2.3 

i-7 



Dietrich x recommends notably larger amounts of protein, 
although he too recommends less for breeding than for fattening 
animals. His figures for fattening pigs are 6.0 to 7.0 per 1000 
up to the age of about 6 months, followed by a gradual reduc- 
tion to 3.3 per thousand at 7 to 8 months. For breeding animals 
his figures are 5.0 to 5.5 up to 6 months of age, gradually dimin- 
ishing from that point to 2.0 at maturity. 

491. General conclusions. — It is apparent from the fore- 
going paragraphs that the evidence regarding the protein re- 

1 Ills. Expt. Sta., Circulars 126, 133 and 153. 



GROWTH 413 

quirements for growth is fragmentary and more or less con- 
flicting. On the one side are investigations like Fingerling's 
on cattle and Just's on sheep (486, 487) which appear to show 
that it is possible for the animal to support what seems a normal 
rate of growth upon a supply of protein little greater than the 
maintenance requirement plus the amount actually stored. 
On the other side stand the results of experiments and observa- 
tions upon the fattening of immature animals, in which rations 
at least approximately equal as to their content of net energy, 
and therefore presumably equally effective for simple fattening, 
have produced a greater increase in weight when they contained 
relatively much more protein than the results of the other class 
of experiments would indicate to be necessary. Further con- 
sideration of this apparent conflict of evidence, however, shows 
that the two classes of experiments are hardly comparable. 

For one thing, the experiments in which a relatively high 
protein supply seemed advantageous were all fattening ex- 
periments. The effect of the feed was measured by the gain in 
live weight, which itself is a somewhat uncertain criterion, 
while a considerable share of this increase was due to a storage 
of fat rather than of protein. Fingerling's and Just's experi- 
ments, on the contrary, relate distinctly to growth and the 
comparisons are based on the actual amounts of protein tissue 
produced, although it must be admitted that any experimental 
errors would probably tend to make the excretion of nitrogen 
appear too low, and therefore the gain of protein too high. 

Another important difference between the two classes of 
experiments lies in the nature of the rations. In the metab- 
olism experiments they were composed largely of commercially 
pure nutrients such as starch, oil, etc., with only the amount 
of roughage necessary to supply bulk, and in particular, the 
variations in the protein supply were effected by changes in 
the amount of commercially pure wheat gluten. In the fatten- 
ing experiments, on the contrary, the higher protein content of 
the rations was obtained by the use of the ordinary protein- 
rich feeding stuffs. What these experiments really show is that 
a larger proportion of these feeding stuffs was advantageous, 
but it does not necessarily follow that this advantage was due 
to the added protein. For one thing such a modification of 
the rations must have affected the ash supply to a certain extent. 



414 NUTRITION OF FARM ANIMALS 

In particular, however, the influence of those accessory sub- 
stances or " growth substances " (498,499) which recent investi- 
gations have shown to play such an important part in condition- 
ing growth is to be considered. It seems not impossible that 
high-protein feeds may in some such way have a stimulating 
effect upon the capacity for growth quite independently of their 
protein content. On the other hand, however, any such stimu- 
lating effect upon growth would be absent in experiments made 
with pure nutrients added to a basal ration of hay or straw, and 
yet a fairly normal rate of increase seems to have been maintained. 
On the whole, one can hardly fail of the impression that the 
requirements for protein as such in growth have been over- 
estimated and that the organism may utilize its protein supply 
more economically than the current feeding standards would 
indicate ; in other words, that the actual protein supply may 
be made considerably smaller than has been supposed before 
it becomes a limiting factor in growth. Until this impression 
is confirmed by more extensive investigation, however, it ap- 
pears the safer course to adhere provisionally to the accepted 
standards, and the protein requirements for growth as estimated 
in Table IV b of the Appendix are based upon those formulated 
by Kellner. 

Ash requirements 

492. Growth involves storage of ash. — The growing animal, 
like the mature one, requires mineral ingredients for the pur- 
poses enumerated in Chapter V (268-272), but in addition to 
this the formation of new tissue and especially of the skeleton 
involves the storage of ash ingredients which must be derived 
from the feed. This is shown clearly by the data recorded in 
§ i (458) regarding the composition of the increase, its ash 
content, aside from one exceptional case, ranging from 1.42 per 
cent to 6.18 per cent. 

493. Rate of storage in growth. — Data regarding the rate 
of storage of mineral elements in growth are not very numerous 
and are largely confined to experiments on the two important 
elements calcium and phosphorus. The principal investiga- 
tions are those of Soxhlet, 1 Neumann, 2 Lehmann, 3 and Weiske 4 

1 i er Ber. Versuch-Station Wien, pp. 101-155. 2 Jour. Landw., 41 (1893), 343- 
3 Landw. Vers. Stat., 1 (1859), 68. 4 Jour. Landw., 21 (1873), 130. 



GROWTH 



415 



on calves, those of Weiske 1 on lambs, and those of Forbes 2 
and of Weiser 3 on pigs. 

Arranging the available results upon the retention of cal- 
cium and phosphorus per 1000 live weight in order of the age of 
the animals, irrespective of the species, gives the following 
showing of the effect of age upon the rate of gain of these two 
elements. It appears that in suckling animals, the rate of 
gain of the ash ingredients, like that of protein and energy 
(463, 464), is relatively high, while there is a distinct falling 
off in the rate as the animal grows older, although not to the 
same extent as in the case of the organic nutrients. 

Table 103. — Daily Retention per iooo Live Weight 



Investigator 



Soxhlet 

Neumann 

Lehmann 

Weiske 

Weiske 

Forbes . 

Weiske 

Weiske 

Weiser . 



Species 


Age 


Calcium 




Days 




Calf 


18* 


0.208 


Calf 


54l 


0. in 


Calf 


149 


0.098 


Calf 


150 


0.073 


Lamb 


177 


0.046 


Pig 


273 


0.042 


Lamb 


292 


0.040 


Lamb 


386 


0.038 


Pig 


— 


0.029 



Phos- 
phorus 



0.118 
0.083 
0.053 
0.059 
0.020 
0.051 
0.031 

0-035 

0.020 



The data of the foregoing experiments hardly afford an 
adequate basis for estimating the ash requirements at different 
ages. As compared with the amounts of mineral elements con- 
sumed in or assimilated from the feed, the body of even a very 
young animal contains a large stock of these substances which 
can be drawn upon to a certain extent to meet any temporary 
deficiency in the feed. It is possible, therefore, that the amounts 
retained in the relatively short periods of the foregoing experi- 
ments may be less than are necessary or desirable for continuous 
normal growth. On the other hand it would appear from 
Forbes' results 4 that, under favorable conditions, ash may be 
stored in the bones in excess of the actual maintenance needs 
and constitute a reserve of mineral matter in the body. The 

1 Landw. Jahrb., 9 (1880), 205. 2 Ohio Expt. Sta., Technical Bui. 5, p. 378. 

3 Biochem. Ztschr., 44 (1912), 279. 4 Loc. ciL, p. 371. 



416 



NUTRITION OF FARM ANIMALS 



fact shown in Chapter IX (435) that more or less storage 
of ash elements may occur even in the mature animal points 
in the same direction. The organism appears far less sensitive 
to fluctuations of its daily supply of ash than to those of the 
organic nutrients because it has relatively a much larger re- 
serve to draw upon. 

494. Total retention during growth. — Some notion of the 
total amounts of mineral elements assimilated during growth 
may be secured by computing from Lawes and Gilbert's anal- 
yses of the ash of the entire bodies of farm animals the 
weights of each ash ingredient contained in them. Thus if 
the live weight at one year old be assumed to be for cattle 400 
kilograms (880 pounds) and for sheep 50 kilograms (no pounds) 
and for a six months' old pig 50 kilograms, then, applying the 
analyses of the half-fat ox, store sheep and store pig respectively, 
the total amounts of mineral elements in the bodies and the 
average daily retention per head (including the stock con- 
tained in the bodies at birth in the case of the sheep and pig) 
would be as follows : — 

Table 104. — Total Retention of Ash Ingredients During Growth 









Gain by 








Calf 


Yearling 


Cattle 


Yearling 


6 Months' 




Cattle 


During 


Sheep 


Old Pig 








ist Year 






Total in body 


Grams 


Grams 


Grams 


Grams 


Grams 


Potassium 


62 


679 


617 


72 


82 


Sodium 


40 


434 


394 


44 


41 


Calcium 


423 


6032 


5609 


472 


386 


Magnesium .... 


17 


203 


186 


17 


16 


Phosphorus .... 


241 


3213 


2972 


259 


233 


Chlorin 


23 


237 


214 


36 


29 


Average retention per day 












and head 












Potassium 


— 


— 


1.64 


0.20 


o-45 


Sodium 


— 


— 


1.08 


0.12 


0.22 


Calcium 


— 


— 


15-37 


1.29 


2. 11 


Magnesium .... 


— 


— 


0.50 


0.05 


0.09 


Phosphorus .... 


— 


— 


8.14 


0.71 


1.27 


Chlorin 


— 


— ■ 


o-59 


O.IO 


0.16 



GROWTH 



417 



In order to compare the figures thus obtained with the results 
recorded in the previous paragraph for the retention during 
short periods, it is necessary to eliminate the influence of vary- 
ing weight by computing the results per 1000. The retention 
of calcium and phosphorus as thus computed agrees very well 
with that found in the balance experiments with the exception 
of Forbes' high result for phosphorus with the pig. On the 
other hand the computed retention of the alkalies is strikingly 
less, a fact for which no obvious reason appears. 

Table 105. — Average Daily Retention per iooo Live Weight 



Potassium 
Sodium . 
Calcium . 
Magnesium 
Phosphorus 



Chlorin | 0.003 



Cattle 

During 

First 

Year 


Sheep 

During 

First 

Year 


0.008 


0.008 


0.005 


0.002 


0.071 


0.052 


0.002 


0.002 


0.037 


0.028 


0.003 


0.004 



Pig Dur- 
ing First 
6 Months 



0.018 
0.009 
0.084 
0.004 
O.051 
0.006 



On the whole it appears that our knowledge of the ash require- 
ments of growing animals, that is, of the actual amounts stored 
up in normal growth, is quite fragmentary and unsatisfactory. 

495. Availability of ash ingredients of feed. — If it is dif- 
ficult to formulate from existing data any trustworthy estimates 
of the ash requirements of growing animals, it is even more 
difficult to make any definite statements regarding the total 
amount of any particular element which must be supplied in 
the feed in order to meet those requirements, although to the 
extent to which the results recorded in the previous paragraphs 
are trustworthy, it is possible to formulate the minimum supply. 
Thus, Weiske's results on sheep show a retention of from 20 
to 35 mgrs. of phosphorus per kilogram of live weight. If 
these figures represent the normal requirements, it is evident 
that a ration containing less than this amount would not supply 
enough phosphorus for normal growth. What surplus above 
this amount is necessary in the feed would depend on the pro- 
portion of the feed phosphorus which is capable of solution in 



2 E 



4i8 



NUTRITION OF FARM ANIMALS 



the digestive tract, and still more upon the effect of other ele- 
ments on the elimination of phosphorus. An amount of this 
element amply sufficient to meet the normal demand when 
supplied in one ration might be quite inadequate in another of 
a different character. 

Since the intestines are the normal path of excretion for 
some ash elements (164, 199), a computation of the digesti- 
bility of these elements in the ordinary sense, by comparing 
the amounts in feeds and feces, gives an entirely false idea of 
their availability. Moreover, it was shown in Chapter IX 
(429-433) that the rate at which mineral elements are lost 
from the body depends to a large degree upon the qualitative 
composition of the ash of the feed, variations in the supply of 
one element sometimes affecting materially the gain or loss of 
another. In particular it was pointed out that the proportion 
of acid and basic elements and to a less degree the ratio of 
potassium to sodium may have striking effects of this sort. 
For example, in Weiser's experiments on pigs (493), the ad- 
dition of 5 grams of calcium carbonate to a ration of iooo 
grams of maize not only changed a loss of calcium into a gain 
but also produced the same effect on the phosphorus balance, 
so that a phosphorus supply which was previously insufficient 
to maintain the body was able to support a material gain. 

Table io6. — Ash Balance or Swine with and without Calcium 

Carbonate 



Maize alone 
In feed 
In feces 
In urine . 
Balance 



Maize and CaCO% 

In feed . . 

In feces . . 

In urine . . 

Balance 



Calcium 



0.1996 



1.0686 



1. 1298 
0.1384 



1.2682 1.2682 
2.1950 



1.2602 
0.0766 
0.8582 

2.1950 2.1950 



Phosphorus 



2.6731 



0.3973 



2.2570 
0.8134 



3.0704 3.0704 

2.8167 

1.6960 
0.2714 

0-8493 

2.8167 2.8167 



GROWTH 



419 



It has been maintained, principally on the basis of Soxhlet's 
experiments on calves (493), that the availability of the ash 
ingredients of milk, and particularly of its calcium and phos- 
phorus, is especially high. The percentages retained in the 
body on the average of the five trials were : — 



Total ash . 

Potassium . 

Sodium 

Calcium 

Magnesium 

Phosphorus 

Chlorin 



53-o 
20.7 
29.1 
97.0 
30-S 
72.5 
3.8 



Neumann's experiments with somewhat older calves (493), 
however, render it evident that the cause of the high retention 
of calcium and phosphorus was the large demand for these 
elements in the body. It can hardly be supposed that these 
elements are less assimilable in the skim milk used in Neumann's 
experiments, yet the percentage retention was scarcely more 
than one-half as great as in Soxhlet's experiments, viz., in the 
experiments on skim milk alone. 



Calcium . 
Phosphorus 



Period i 



47-8% 
.Si.i% 



Period 3 



44-5 % 
42.7 % 



Period 5 



44-1 % 
41.8% 



The older animals obviously required less of these elements 
and therefore excreted the excess, the phosphorus in the urine 
and the calcium in the feces. 

Lehmann's and Weiske's experiments (493) with older calves 
on mixed rations showed a percentage availability of the phos- 
phorus and calcium fully as great as that observed for skim 
milk in Neumann's experiments, and here too the natural con- 
clusion is that the demand for these elements in the body, 
rather than any lower availability per se, is the cause of the less 
assimilation. It is well established that the inorganic phos- 
phates may be quite completely assimilated, and Fingerling 1 
1 Landw. Vers. Stat., 79-80 (1913), 847; 86 (1915), 75. 



420 NUTRITION OF FARM ANIMALS 

has shown the same thing to be true of a variety of organic 
phosphorus compounds, as well as of the phosphorus of con- 
centrated feeding stuffs, while in case of roughages * an avail- 
ability of approximately 50 per cent was observed. These 
facts throw some doubt on Kellner's conclusion that the feed 
should contain two or three times the quantities of mineral 
elements which would normally be stored in the body. 

496. Effects of deficiency of ash. — But while it seems 
scarcely possible to make any definite quantitative statements 
regarding the necessary ash supply of growing animals there is 
abundant evidence of the evil effects of an insufficient supply. 
In particular, a deficiency of calcium, as already indicated, 
may have serious consequences both directly and on account of 
the fact that such a deficiency generally connotes an acid ash 
(431). 

Kellner 2 cites experiments by.Roloff and by Voit, in which young 
dogs and pigs receiving feed poor in calcium showed deficient growth 
and developed severe pathological symptoms, the skeleton showing 
a notable deficiency in ash ingredients (Rachitis) . Forbes 3 has col- 
lected a large number of experiments on this subject in some of which 
marked effects on the composition of the bones were observed while 
in others these effects were not very distinct. In still more recent 
experiments by Weiser 4 upon pigs, a diet deficient in calcium re- 
stricted the growth and produced a skeleton containing an excess of 
water and organic matter and deficient in ash. Contrary to the re- 
sults of Aron (428) the bone ash on the calcium-poor rations was 
deficient in calcium and contained an excess of alkalies, especially 
sodium. 

Of farm animals, pigs are most likely to suffer in this way, 
partly because their growth is relatively rapid and partly be- 
cause they often receive almost exclusive grain rations which 
are apt to be low in calcium (431). Henry 5 has shown that 
supplementing such rations with calcium phosphate or car- 
bonate results in the production of heavier and stronger bones, 
and Burnett 6 has confirmed these results. Hart and McCol- 

1 Biochem. Ztschr., 37 (1911), 266. 

2 Ernahrung der landw. Nutztiere, 6th Ed., p. 177. 

3 Ohio Expt. Sta., Tech. Bui. 5, pp. 384-390. 

4 Biochem. Ztschr., 66 (1914), 95. 

6 Wis. Expt. Sta., 6th Rpt., pp. 6-41 ; Bui. 25. 
6 Neb. Expt. Sta., Buls. 94 and 107 and 23d Rpt, 



GROWTH 421 

lum x found that confined pigs on a ration of maize alone and 
drinking distilled water failed to grow, while the addition of an 
artificial mixture of salts enabled nearly normal growth to be 
made. 

With cattle and sheep a deficiency of calcium is not usually 
to be feared, since roughages are usually rich in this element. 
Straw and roots, however, are rather low in calcium and so are 
certain by-product feeds, especially those like gluten feed and 
meal, distiller's grains, etc., which have been subject to ex- 
traction with water. 

497. Forms of phosphorus. — A much discussed question is 
that of the relative value of organic and inorganic phosphorus 
compounds. It was stated in Chapter V (258), that the animal 
body is apparently able to synthesize its organic phosphorus 
compounds from inorganic phosphorus. Forbes 2 has given 
a very complete review of the literature of this subject. His 
general conclusion is that it has not been proven that a supply 
of organic phosphorus is essential, although he regards the 
proof that inorganic phosphorus can serve all the purposes for 
which any animal needs phosphorus as being incomplete. As 
regards the relative efficiency of the two, the facts already noted 
in Chapter IX (437, 438) and in the following paragraphs, re- 
garding the importance of accessory substances, in particular 
the so-called growth substances, in nutrition strongly suggest 
that the apparent superiority of organic phosphorus which has 
been observed in some experiments may have been due to the 
presence of such substances accompanying the organic phos- 
phorus compounds and not to the latter as such. 



Accessory substances 

498. Relation of fats to growth. — It was mentioned in 
Chapter V (265), in considering the functions of the nutrients, 
that it had apparently been shown that the presence of a certain 
minimum amount of fat (or at least of ether-soluble sub- 
stances — lipoids) was necessary for growth. Later investi- 
gations, however, have led to a different interpretation of these 

1 Jour. Biol. Chem., 19 (1914), 373. 

2 Ohio Expt. Sta., Tech. Bui. 5, pp. 318 to 365- 



422 NUTRITION OF FARM ANIMALS 

earlier results. As the technique of experimentation with iso- 
lated nutrients has been developed by the work of Rohmann, 
McCollum, Osborne and Mendel and others, it has become 
evident that it is not the lipoids as such but some substance or 
substances associated with them which are essential to con- 
tinued growth. On the one hand, growth has been maintained, 
for a considerable time at least, on a practically fat-free diet, 
while on the other hand it has been shown that by no means 
all fats are capable of exerting this favorable effect on growth. 

Both McCollum and Osborne and Mendel have found that rats fed 
mixtures of purified nutrients containing no fat may grow normally 
for a considerable time, but after about 75 or 100 days, and after 
reaching perhaps § of the mature weight, there is a more or less abrupt 
cessation of growth followed by a speedy decline in weight. Sub- 
stantially the same result ensues when certain forms of fat (lard, beef 
fat, olive oil, almond oil) are added to the ration, but if, on the other 
hand, purified butter-fat, cod liver oil or certain other fats be added 
to the ration of an animal which has ceased to grow and begun to 
decline in weight this decline is promptly stopped and practically 
normal growth resumed. These results indicate the existence of two 
groups of fats, one of which aids growth while the other does not. 
Evidently, therefore, the growth supporting property does not reside 
in the glycerids themselves but in some accompanying substances. 

499. Growth substances. — On the basis of later investiga- 
tions, McCollum * rejects Funk's hypothesis of the existence 
of numerous specific " vitamins " and distinguished only two 
growth substances (or classes of substances) , both of which are 
essential to growth. One, lipoid-soluble, which he calls fat- 
soluble A, is associated with certain fats, while the other, called 
water-soluble B, is soluble in water and apparently never asso- 
ciated with fats. The fat-soluble A is absent from all vege- 
table fats thus far examined. It is present in small but in- 
sufficient amounts in the grains but appears to be relatively 
abundant in the leaves of plants. 

That other factors than these specific growth substances may 
markedly influence growth is, however, apparent from recent ex- 
periments by Hart and McCollum 2 who found that the freedom 

1 Jour. Biol. Chem., 23 (1915), 181 and 231 ; 25 (1916), 105 ; Amer. Jour. Physiol., 
41 (1916), 333 and 361. 

2 Jour. Biol. Chem., 19 (1914), 373. 



GROWTH 423 

of a small paddock in which they can root stimulates the growth 
of pigs to a degree quite out of proportion to the amount of 
actual feed thus obtained. Furthermore, they have shown 
that, with both pigs and cows (438), rations consisting exclu- 
sively of wheat products seem to have a direct effect in hinder- 
ing growth. The subject is one which is hardly ripe for dis- 
cussion, but it opens up an interesting field for investigation, 
while it emphasizes the importance of variety in rations. 

No data have been published regarding the percentage 
utilization of the feed actually consumed in these experiments 
as measured by the amount of growth actually made on the 
inadequate rations. 



CHAPTER XII 
MEAT PRODUCTION 1 

§ i. Nature of Meat Production 

500. Definitions. — By " meat " is understood in a general 
way the flesh of an animal as distinguished from the skeleton 
on the one hand and the internal organs, hide and other offal 
on the other. Meat in this general sense is separable mechani- 
cally into adipose tissue (" fat ") and lean meat, both of which, 
but especially the latter, are of somewhat complex composition. 

The adipose tissue (94) consists of connective tissue in which 
a greater or less accumulation of fat has taken place and is 
essentially a reserve of non-nitrogenous, energy-yielding ma- 
terial. The lean meat, or meat in the narrower sense (86), 
consists primarily of muscular tissue along with more or less 
fat, and its characteristic ingredients are the proteins. 

501. Proportion of fat and lean in carcass. — The proportion 
of lean meat to fat tissue in the carcass is naturally quite vari- 
able, depending somewhat upon the age but chiefly on the feed- 
ing of the animal, insufficient nutrition reducing the store of fat 
in the body to a minimum while heavy feeding may cause the 
production of large amounts of it. Thus Lawes and Gilbert 
found the proportion of fat in the carcasses of the ten animals 
analyzed by them (97) to vary from 15.3 to 48.3 per cent. 
Jordan observed a range of 18.80 to 24.62 per cent in steers 2-2 J 
years old. Tschirwinsky reports the extremes of 10.39 an d 
40.92 per cent in pigs, while Wilson found a minimum of 1.31 
per cent in new-born pigs. Atwater 2 gives the following as 
the average composition of a side of beef of medium fatness : — 

1 The discussions in this chapter follow, to a considerable extent, those presented 
by the writer in U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908). 

2 U. S. Dept. Agr., Office Expt. Stas., Bui. 21 (1895), p. 35. 

424 



MEAT PRODUCTION 



425 



Table 107. — Average Composition of a Side of Beef of 
Medium Fatness 



Water 
Protein 
Fat . 
Ash . 



% 



54-77 

17.20 

27.07 

0.96 



100.00 



Lean cuts of meat, however, may contain much less fat than 
is indicated by the foregoing statement. Thus Grindley and 
Emmett l analyzed seven samples of beef round from which the 
visible fat had been removed. The minimum figure for fat was 
3.19 per cent in the fresh substance, or 12.29 per cent of the 
dry matter. The average of the seven analyses was as fol- 
lows : — 

Table 108. — Average Composition of Seven Samples of Beef Round 
with Visible Fat Removed 



In Water-free 
Substance 



Water . . 
Ash . . . 
Protein 
Extractives 
Fat . . . 




Voit found in the carefully prepared lean meat which he 
used as representing substantially protein feed, and which had 
been most painstakingly freed from all visible fat, 0.91 per cent 
of ether extract in the fresh substance, equal to 3.77 per cent of 
the dry matter. 

The term meat commonly suggests to the mind the muscular 
tissue of the animal, and has become almost synonymous with 

1 Ills. Expt. Sta., Bui. 162. 



426 NUTRITION OF FARM ANIMALS 

a protein diet. It is evident, however, that the commercial 
growing of meat may involve the production of considerably 
more fat than protein and that, in so far as this fat is actually 
consumed, meat is far from being the distinctively protein 
food which it is. ordinarily considered. Thus the so-called 
" nutritive ratio " of the average side of beef, calculated in the 
usual manner, is about i : 3.5. On the other hand, however, it 
is equally true that the proteins of meat are the distinctive in- 
gredients for the sake of which it is produced and eaten, while 
the fat, although a valuable nutrient, is to a certain extent sub- 
sidiary and accidental. 

502. Processes involved. — Corresponding in a general 
way to the two main constituents of commercial meat, viz., 
muscular tissue and adipose tissue, two distinct physiological 
processes are involved in meat production, viz., growth and 
fattening. 

Growth. — The animal at birth is usually regarded as 
unfit to serve as human food. Moreover, even were this 
not the case it would be in the highest degree uneconomic 
to fail to utilize the marked assimilative powers of the 
young animal for the production of body tissue (meat) 
from feed. Consequently the production of meat involves 
more or less growth in all cases. This may, for special reasons, 
be concluded early, as in the production of lamb or veal, but as 
a whole the world's commercial meat supply is derived from 
animals at least approaching maturity. This growth of animals 
from birth to approximate maturity consists essentially of an 
increase in the protein tissues (457), the rate of which is es- 
sentially determined by the nature and individuality of the 
animal and can at most be but slightly stimulated by an in- 
creased protein supply (403, 484). 

Fattening. — Fattening, on the contrary, is a process which, 
in a given animal at least, is largely under the control of the 
feeder. Substantially it is dependent on the quantity of feed 
consumed by the animal in excess of the requirements for 
maintenance and growth, and there is lacking any definite proof 
that the actual storage of energy in the form of gain for a given 
amount of excess feed is seriously affected either by the age or 
the individuality of the animal. Fattening, therefore, may 
take place at any age, although of course the greater demand 



MEAT PRODUCTION 427 

for material for growth in the young animal tends to reduce the 
proportion of the feed available for fattening. 

The prime object of fattening (446) is an improvement in 
the quality of the meat by the deposition of fat between the 
fibers of the meat, and to some extent by increasing the ex- 
tractives of the meat itself. The large deposits of fat about 
the internal organs and under the skin are incidental to this and 
are to a certain extent a waste. The subcutaneous fat affords 
a convenient index to the quality of the meat, and of course 
the adipose tissue of the carcass is of some value, but these fat 
deposits largely represent the price paid for the improved qual- 
ity of the meat proper. It is not impossible that the traditions 
of the market may cause the process of fattening to be pushed 
beyond what is necessary. 

This improvement in quality may be, and to a considerable 
extent is, secured by a comparatively short period of high 
feeding after growth has been nearly completed. It is obvious, 
however, that no sharp line can be drawn between the pro- 
cesses of growth and fattening. A calf or yearling may be 
fattened while growing, and a two-year-old steer will continue 
to grow to some extent while being fattened. The two pro- 
cesses shade into each other and economic considerations will 
decide whether they shall be carried on more or less simultane- 
ously by a single producer or at different times by two different 
individuals. 

In brief, meat production may be defined as a combination 
of growth and fattening, which may be either simultaneous or 
successive, but the production of protein tissue is the primary 
object in view, while the accumulation of fat, although adding 
to the nutritive value and to the palatability of the meat, is more 
or less a secondary matter. The purpose of the present chapter 
is to consider the application of the principles of growth and 
fattening discussed in the two preceding chapters to this branch 
of food production. 

503. Factors of meat production. — From the economic 
point of view, the meat producing animal may be looked upon 
as a mechanism by means of which the raw material contained 
in the various feeding stuffs is converted into the finished prod- 
uct for human consumption. Regarding meat production, 
then, as a manufacturing process, the amount and quality of 



428 NUTRITION OF FARM ANIMALS 

the production obtained is plainly dependent upon three factors : 
first, the efficiency of the mechanism ; second, the amount and 
quality of the raw material supplied; third, the conditions 
under which the mechanism is operated. 

§ 2. The Animal as a Factor in Meat Production 

Of the three factors just mentioned, the animal may fairly 
be said to be the one of prime importance. The success of the 
feeder depends primarily upon the capacity of his animals to 
convert profitably large amounts of raw materials into a 
finished product of high quality. 

Early maturity 

504. Definition of maturity. — Much stress is rightly laid 
upon the importance of early maturity in meat production, al- 
though the term is used in two more or less distinct senses. 

Strictly speaking, a mature animal is one which has completed 
its growth — i.e., one in which the increase of protein tissue has 
reached its natural limit. In this sense, that one of two animals 
which reaches this natural limit first is the earlier maturing. 
With animals which reach substantially the same limit of size, 
this conception of early maturity is, of course, synonymous 
with a greater absolute rate of protein growth (460), while if the 
latter be expressed relatively to the weight of the animal, as 
in previous pages, the same thing is true regardless of size. 

The term early maturity, however, is used also in a quite 
different sense, referring to the conformation of the animal rather 
than to completed growth. Thus, if a steer at 22 months has 
attained the typical beef form and reached sufficient size to 
meet the demands of the market, he is said to be mature. Ob- 
viously, this does not mean that he has completed his growth, 
but simply that he has made sufficient growth to furnish market- 
able meat. This conception of maturity, in other words, is 
commmercial rather than physiological. It is important to 
note, however, that it involves a physiological element. A 
certain size of carcass as well as a certain conformation is de- 
manded, and to reach this at an early age almost necessarily 
implies a greater rate of growth, whether measured physiologi- 



MEAT PRODUCTION 429 

cally by increase of protein tissue or practically by gain in 
weight. 

In whichever sense the term maturity is used, however, the 
matter reduces itself to the question of rate of growth. The 
greater the initial impulse to growth, the sooner, other things be- 
ing equal, will the animal complete his growth, while if the rate 
of growth can be made sufficiently rapid the desired accumula- 
tion of meat, and consequent weight, may be reached before 
physiological maturity. In other words, the rate of growth may 
be looked upon as expressing the capacity of the machine, since, 
as was stated in Chapter XI, it is substantially determined 
by biological factors and is apparently little affected by the feed 
supply, provided only that the latter is adequate. 

505. Economic significance. — There seems no reason to 
suppose that there is any material difference as regards physio- 
logical economy between rapid growth and slow growth ; that 
is, there is no reason to suppose that the storing up of certain 
amounts of protein and energy in the body of an animal in one 
month requires any greater or any less total feed supply, in 
addition to the maintenance requirement, than the storing up of 
the same amounts in the two months' time, except as heavy 
feeding may diminish the percentage digestibility of the ration 
(722). In other words, it may be assumed that if a gain of one 
pound in live weight contains 2500 Calories of energy, the ra- 
tion must supply that amount of net energy above the main- 
tenance requirement within the time required to make the 
gain, whether that time be one day or three. 

From the economic point of view, however, there is a very 
important difference which explains the stress laid upon early 
maturity in meat-producing animals. It is plain that, other 
things being equal, the animal which inherits the greater initial 
impulse to growth, and in which that impulse dies out the more 
slowly, will reach either physiological maturity or a given size 
and weight sooner than the one in which that impulse is less. 
It makes a very material difference, however, to the producer 
of beef cattle, for example, whether a calf weighing 100 pounds 
at birth has the capacity to reach a weigh of 1200 pounds at 
two years old, or whether he requires three years to do it. This 
is not, however, because there is any material difference in the 
amount of feed which the animal requires to manufacture the 



430 NUTRITION OF FARM ANIMALS 

noo pounds of increase. The difference as regards feed cost 
comes in the expenditure for maintenance, since each pound 
of gain, as well as the original ioo pounds, must be maintained 
from the time it is laid on until maturity. The animal, then, 
which has the higher rate of growth and which matures in 
two years costs the owner a notably less expenditure for feed 
than the one maturing in three years, to say nothing of the 
saving in cost of attendance and in interest on the investment. 

Age 

506. Influence on cost of production. — It is an undisputed 
fact that gain is made more rapidly and more cheaply by the 
younger as compared with the older animal. This is true both 
in growth proper and in the commercial fattening of partly 
mature animals. 1 

On the other hand, it was shown in Chapter XI (472-476) that 
there is no experimental evidence that the capacity of the young 
animal for making a more rapid gain is due to any greater 
physiological economy in the conversion of surplus digestible 
material into tissue, while it has also been established (720) 
that the digestive power of the young animal is not materially 
different from that of the mature animal. As regards protein, 
the indications are that the loss of nitrogenous material in the 
actual conversion of feed protein into body protein is not or- 
dinarily great and is no greater in the old than in the young 
animal, while as regards energy it was shown that the proba- 
bilities are in favor of the view that its utilization is less rather 
than greater in the younger than in the older animal. 

507. Causes of greater economy. — More or less confusion of 
thought has resulted from this apparent conflict of evidence, 
while feeding experiments like those cited by Henry and Morri- 
son have been made the basis of unwarranted inferences as to 
the greater digestive and assimilative powers of young animals. 
This confusion has arisen to a large degree through failure to 
distinguish between physiological and commercial economy 
and it is important to secure a clear conception of the elements 
of the commercial superiority of the younger animal. 

1 Compare Henry and Morrison, Feeds and Feeding, 15th Ed., pp. 431-434, 512, 
568-572. 



MEAT PRODUCTION 431 

508. Difference in feeding stuffs. — The difference in the 
character of the feed consumed by the animal at different ages 
must not be overlooked. The very young animal subsists on 
milk (or milk substitutes). As it grows older and begins to 
consume solid feed, the latter must be at first of a rather con- 
centrated character and highly digestible while, with advancing 
maturity, the ration is likely to consist to an increasing extent 
of coarser and more bulky materials. It is evident that to 
make a direct comparison between animals receiving such dif- 
ferent rations on the basis of the dry matter of the latter is to 
ascribe to differences in the animals what is really due to differ- 
ences in the feed. The ration of the younger animal will usually 
have the higher percentage digestibility, while at the same 
time it may cause a smaller expenditure of energy in the pro- 
cesses of digestion and assimilation, so that the net energy values 
of the rations per unit of dry matter are unequal. That an 
animal shows a greater rate of gain on milk than later on a 
mixed ration of grain and roughage does not necessarily show 
that the younger animal made any more efficient use of the 
materials actually resorbed, but may be simply because it re- 
ceives more actual feed (net energy) in a unit of dry matter. 

509. Difference in composition of gain. — It must also be 
remembered that the cheaper gain made by the younger an- 
imal means gain in live weight and that, as shown in Chapter 
XI (458), this increase is of inferior food value as compared 
with that of the more mature animal and represents the storage 
of less energy, since it contains more water and a larger pro- 
portion of protein to fat in its dry matter. A greater increase 
in live weight, even on perfectly comparable rations, therefore 
may be compensated for by the lower quality of that increase. 
Gain by the younger animal is, so to speak, more dilute. 

510. Feed consumption. — A third important factor, es- 
pecially when the animal is not pushed to the limit of his capac- 
ity, is the relatively greater consumption of feed by the younger 
animal. While the individual consumes more feed per head as 
it grows older, the consumption per unit of live weight and in 
particular per unit of body surface decreases. For example, 
in Henry's averages for swine and in Weiske's experiments on 
growing lambs cited in Chapter XI (481 b, 487), the total feed 
consumption was : — 



432 NUTRITION OF FARM ANIMALS 

Table 109. — Relation of Weight of Pigs to Feed Consumed 







Daily Feed 








Per 100 Lb. 


Live Weight 




Actual Aver- 
age Weight 








Range of Weight 


Per Day 


In Proportion 
to Weight 


In Proportion 
to Surface 


Pounds 


Pounds 


Pounds 


Pounds 


Pounds 


15 to 50 


38 


2.2 


6.0 


4.9 


50 to IOO 


78 


3-4 


4-3 




100 to 150 


128 


4.8 


3-8 




150 to 200 


174 


5-9 


3-5 




200 to 250 


226 


6.6 


2.9 




250 to 300 


271 


7-4 


2.7 




300 to 350 


320 


7.5 


2.4 


3-45 



Table iio. — Feed Consumption by Lambs 



Period I 
Period II . 
Period III . 
Period IV . 
Period V . 
Period VI . 
Period VII 
Period VIII 
Period IX . 
Period X . 



Live Weight 



Kgs. 
20.5 

25-5 
28.9 
32.6 
35-0 
35-3 
38.0 

40.5 
39-o 

57-5 



Digestible Organic Matter 

Eaten per 50 Kgs. Live 

Weight 



In Proportion 
to Weight 



Grams 

I059 
1029 
870 
850 
757 
755 
710 
681 
690 
549 



In Proportion 
to Surface 



Grams 
787 



575 



But the maintenance requirement is approximately propor- 
tional to the body surface. Consequently the feed consump- 
tion as the animal grows older does not keep pace with the in- 
crease in its maintenance requirement, so that a constantly 
diminishing proportion of its feed is available for productive 
purposes. For example, in Periods I and X respectively of 
Weiske's experiment it may be computed that the metaboliz- 



MEAT PRODUCTION 433 

able energy of the rations consumed and the approximate 
maintenance requirements per day and head were : — 

Table hi. — Diminishing Availability of Feed 



Metabolizable Energy 



In ration 

Required for maintenance 
Available for gain . . . 



Period I 



1568 Cals. 
807 Cals. 
761 Cals. 



Period X 



2209 Cals. 

1613 Cals. 

596 Cals. 



In Period I, 48.5 per cent of the metabolizable energy of the 
ration was available for growth as compared with only 27 per 
cent in Period X. 

In brief, then, the undisputed superiority of the young animal 
as regards the amount of feed required to produce a unit of 
increase may be reasonably ascribed : — 

First, to the fact that his feed is often of a more concentrated 
nature, containing a greater proportion of digestible matter and 
perhaps causing a smaller expenditure of energy in connection 
with its digestion and assimilation. 

Second, to the fact that the gain of live weight in the young 
animal contains a less percentage of dry matter and especially 
of fat and therefore represents the storage of less energy than 
the same increase in the older animal. 

Third, that the total feed consumption of the animal, espe- 
cially upon the more bulky feeds generally used for simple 
growth, may not increase as rapidly as the maintenance re- 
quirement, so that an increasing proportion of the feed is 
required simply for maintenance and is unavailable to produce 
increase. 

511. Production of lean meat. — The difference in the nature 
of the gain made at different ages which, as has just been shown, 
is a material factor in determining the cost of gain in live weight, 
is of even greater importance in another aspect of the matter. 

As shown in Chapter XI (460-463), the capacity for growth 
in the stricter sense, i.e., for increase of protein tissue, is especially 
characteristic of the young animal and decreases rapidly as he 
grows older, while it does not appear that it can be materially 

2 F 



434 



NUTRITION OF FARM ANIMALS 



stimulated by the protein supply in the feed. It is of the high- 
est economic importance, therefore, to utilize to the full the 
ability of the young animal to lay on protein tissue. In the early 
stages of growth, he is able to utilize a relatively abundant supply 
of feed protein which, if given to an older animal, would largely 
undergo protein katabolism and be lost so far as growth is 
concerned, while at the same time the total feed per head re- 
quired for maintenance is smaller. The feeder cannot afford 
to stint the protein supply of the young animal, while the 
earlier the process of growth can be completed or approach 
nearly enough to completion to satisfy market demands, the 
more economically will it be conducted. 

The conclusions regarding the rate of increase of protein 
tissue considered in Chapter XI are, however, derived chiefly 
from determinations of the gain or loss of total nitrogenous 
matter, including, besides the edible portion, the protein of the 
skin, hair, hoofs, horns and other epidermal tissue, of the in- 
ternal organs and of the skeleton. It is important, therefore, 
to inquire into the rate of increase of the edible portion of the 
carcass. 

Table 112. — Gain of Fat-free Lean Meat and Total Protein by 

Lambs 



Lot 





Length 


Period 


of 




Period 




Days 


f I and II 


203 


III and IV 


259 


IV 


175 


f I and II 


189 


IIH 


J 47. 



Character 
of Ration 



Growing 

Growing 

Fattening 

Fattening 

Fattening 



Aver- 
age 
Age 
of 
Ani- 
mals 



Days 

290 

521 

745 
290 

458 



Gain per Week 
and Head 



Fresh 


Total 


Fat- 


Dry 


free 


Protein 


Meat 


(Esti- 




mated) 



Kilo- 
grams 

O.I14 

•053 
.042 
.130 
.040 



Kilo- 
grams 

O.056 
.031 
.029 
.077 
.026 



While it may be fairly assumed that the increase of edible meat 
will be in a general way proportional to the increase of total protein, 
it is equally clear that there may be considerable departures from 
the average. Unfortunately, however, the data upon this point are 



MEAT PRODUCTION 



435 



scanty, owing to the laborious and expensive nature of such experi- 
ments. About the only results available are those of Kern and 
Wattenberg on lambs and those of Jordan on steers, that is, these are 
the only ones which permit of a comparison of the rate of growth of 
similar animals in successive periods. Both these experiments have 
been outlined in Chapter XI (458) . Table 112 shows the gain of fat- 
free lean meat in Kern and Wattenberg's experiments as compared 
with the estimated gains of total protein. The term "meat" refers 
only to the meat of the "butcher's pieces," freed from sinews and 
coarser connective tissue by passage through a meat grinder. The 
production of fat-free lean meat was, in general, parallel to that of 
total protein, diminishing with advancing maturity. Apparently, 
however, the rate of gain of total protein diminished less rapidly than 
that of edible meat. 

Jordan's experiments include a comparison of the weights and 
chemical composition of two pairs of animals at the end of twenty- 
seven months' and seventeen months' feeding respectively. The pro- 
tein of the lean meat after mechanical separation from the fat tissue, 
and the total body protein, were as follows : — 

Table 113. — Gain of Protein by Cattle 



No. of Animal 


Average Age 


Protein of 
Lean Meat 


Total Protein 
of Body 


2 

1 


32 months 
22 months 
Gain in 10 months 
Gain per day 

32 months 
22 months 
Gain in 10 months 
Gain per day 


Pounds 

42.13 
37.96 l 

4.17 
.0128 


Pounds 

167.94 
136.30 
31.64 
.0971 


3 

4 


43- 2 4 
35-o8 

8.16 
.0261 


161.38 
126.30 

35-o8 
.1123 



So far as conclusions can be safely drawn from these few 
results, it would appear that the rate of gain of lean meat runs 
parallel to that of total protein and like the latter diminishes 
with age, the diminution being somewhat more rapid in the for- 
mer case than in the latter. At all ages the storage of total 

1 Nos. 1 and 4 were somewhat lighter animals than Nos. 2 and 3. The protein 
content has been computed to the live weight of the heavier animal in each case. 



436 NUTRITION OF FARM ANIMALS 

protein (or, more exactly, the increase in the fat-free body) 
considerably exceeds the gain of lean meat proper and with in- 
creasing maturity this difference seems to become relatively 
greater. 

512. Best age for fattening. — While meat production in 
the narrower sense of increase of protein tissue is confined to 
the immature animal, the improvement of its quality by the 
fattening process is an essential part of commercial meat pro- 
duction. Fattening, however, may be effected at practically 
any time in the life of the animal. Assuming that an animal 
is to be in the hands of the same owner from birth until 
slaughter, at what stage should the distinctively fattening 
process as distinguished from growth be begun? 

It is evident that the beginning of the fattening process may 
be delayed too long. To take the extreme case, it would be 
obviously uneconomical first to grow an animal to full maturity 
and then to add a fattening period. While there is no reason 
to suppose that the amount of feed actually expended in the 
production of a unit of fat would be materially greater than if the 
fattening were conducted during the latter part of the growing 
period, the expenditure for maintenance, care, interest, etc., 
would be simply so much added to the cost of production. On 
the other hand, heavy fattening rations, containing large amounts 
of non-nitrogenous nutrients, even if they do not interfere with 
the growth of young animals, are uneconomical, tending either 
to overload the meat with fat or toward the accumulation of 
cheap internal fat, and making the animal ripe for the butcher 
before his capacity for producing lean meat has been properly 
utilized. A limited market exists, of course, for fat lambs and 
veals ; but for the production of the world's meat supply it is 
important to utilize the capacity for growth up to a point at 
least approaching maturity. Too early fattening tends to 
produce an animal which, even if not of inferior quality, must 
be maintained in a fat condition until the growth of lean meat 
has had an opportunity to overtake that of fat. Plainly the 
beginning of the fattening should be so timed that it will be 
completed by the time the rate of gain of lean meat ceases to be 
profitable under the existing market conditions. 

The period in the life of the animal at which fattening should 
begin, then, will depend upon its inherited capacity for growth, 



MEAT PRODUCTION 437 

i.e., its rate of growth as defined on previous pages. If this is 
rapid, as, for example, in the improved breeds of swine especially 
and to a somewhat less extent with cattle and sheep, it may be 
practicable to begin the fattening almost from birth, the innate 
tendency to growth assuring sufficient size and weight by the 
time good marketable condition is attained. To secure this 
result, however, it is necessary to use rations containing large 
amounts of easily digestible feed in a small bulk and such 
rations are necessarily comparatively expensive. Moreover, 
growth as well as fattening requires an expenditure of feed 
energy, and as appeared in Chapter XI (473-476) a not incon- 
siderable one. The capacity of an animal to consume feed, how- 
ever, is limited and when a relatively young animal is put on 
full feed, the more growth he makes the less feed will remain for 
fattening. This corresponds with the experience of practical 
feeders that mature animals will reach a higher condition in a 
given time than the young ones. 

Under present economic conditions, as a rule, only the best 
grade of animals having to a high degree the quality of early 
maturity can be profitably handled in the way just indicated. 
With animals inferior in this respect, the more economical pro- 
cedure usually is a period of growth upon comparatively cheap 
rations, consisting to a considerable extent of roughage, followed 
by a relatively short period of intensive fattening, beginning, 
however, before the capacity for growth has been entirely lost. 
The economy lies, of course, in the possibility of supporting 
growth and maintenance upon relatively cheap feeds during 
the longer time necessary in the case of inferior animals and 
will depend to a large extent upon the relative costs of feeding 
stuffs. The actual feed cost of the fattening itself is likely to 
be about the same in either case. 

For the individual who raises and fattens his own animals, 
then, it would appear to be economical, so far as the feed cost 
is concerned, to use as early maturing animals as possible and 
to push them so as to fit them for market at as early an age 
as they are capable of. 

When, however, as is notably the case in beef production, the 
rearing of animals and their fattening for market are in dif- 
ferent hands, other important economic considerations enter 
in to modify this conclusion. In this case the business of 



438 NUTRITION OF FARM ANIMALS 

the feeder is substantially to enhance the quality of the 
meat, and the profit of the transaction depends to a consider- 
able extent upon the difference between buying and selling 
prices, and includes a large element of speculation. While it 
is true that the animal which still retains more or less capacity 
for growth will make the cheaper gains, nevertheless, if the 
market price of such animals is relatively high compared with 
that of more mature animals it may be more profitable as a 
business proposition to feed older animals, even though the 
feed cost per pound of gain is higher. 

Condition 

513. Decreasing gains in fattening. — It is generally admitted 
that in the case of the nearly mature fattening animal the rate 
of gain in live weight decreases as the fattening progresses until 
a limit is reached beyond which the increase, if obtained at all, 
is slow and very costly. Several causes are responsible for 
this : — 

First, the maintenance requirement of the animal increases 
with its gain in weight (393). The capacity of the digestive 
organs, however, undergoes no corresponding increase, and 
consequently the amount of excess feed is correspondingly re- 
duced and its proportion in the ration made less, so that the 
total feed requirement per unit of gain will be greater. 

Second, the appetite of well-fattened animals not infrequently 
diminishes, resulting in a lessened consumption of feed. This 
again has a double effect, diminishing the total amount of excess 
feed available and reducing the ratio of excess feed to total feed. 

Third, a unit gain in live weight toward the close of the 
fattening period represents a larger storage of energy than the 
same gain at the beginning (452). 

514. Effect on economy of gain. — For all these reasons it 
is natural that the " condition " of the animal — that is, its 
state of fatness — should have a marked effect on the rate and 
economy of gain. Georgeson l reports the following results 
for a lot of 3-year-old grade Shorthorn steers, the number of 
days stated in the table meaning in each case the number from 
the beginning of the feeding : — 

1 Kansas Expt. Sta., Bui. 34, p. 95. 



MEAT PRODUCTION 439 

Table i 14. — Grain Consumed by Steers per Pound of Gain 



Number of Days Fed 



56 
84 
112 
140 
168 
182 



Grain Consumed 

per Pound of 

Gain 



Pounds 

7-30 
8.07 
8.40 
9.01 
9.27 
10.00 



Henry 1 reports the following similar results for fattening 
swine : — 

Table 115. — Influence of Length of Fattening Period on the 
Feed Consumption and Gain of Hogs 





Average 


Average 


Feed 
Eaten 


Feed for 100 Pounds 
of Gain 




Weight 


Gain 


Week per 




By Four- 








Hog 


By Weeks 


Week 
Periods 




Pounds 


Pounds 


Pounds 


Pounds 


Pounds 


First week .... 


222 


11.4 


41 


362 




Second week . 




235 


13-3 


48 


362 


418 


Third week 




246 


10.5 


5o 


475 




Fourth week . 




257 


10.7 


50 


473 




Fifth week 




270 


13-9 


51 


368 




Sixth week 




281 


IO.I 


51 


5io 


461 


Seventh week 




294 


J3- 1 


51 


39 1 




Eighth week . 




303 


8.9 


51 


572 




Ninth week . 




313 


10.5 


52 


499 




Tenth week . 




322 


8.9 


52 


S87 


559 


Eleventh week 




332 


9.6 


52 


549 




Twelfth week . 




340 


8.8 


52 


598 





On the other hand, Mumford, 2 in large-scale feeding experi- 
ments with cattle, has failed to note any such marked diminution 



1 Feeds and Feeding, 10th Ed., p. 510. 



2 Ills. Expt. Sta., Bui. 103, p. 57. 



440 NUTRITION OF FARM ANIMALS 

of the gain during the later stages of feeding as had been generally 
found by other experimenters. 

There is no sufficient evidence on record to show whether or 
not the actual percentage utilization of the excess feed dimin- 
ishes with the advance of fattening. 

Breed and Individuality 

That both those inherited qualities which characterize the 
recognized meat breeds and the individual differences between 
single animals are important factors in the economy of meat 
production is generally recognized. It is a fact of common 
observation that marked differences exist between individual 
animals as regards the return which they yield for the feed con- 
sumed, but the reasons for these differences have not always been 
clearly seen, and in particular there has been a tendency to 
assign them to physiological causes, such as difference in di- 
gestive or assimilative power, and some unwarranted con- 
clusions on these points have gained currency. 

515. Digestive power. — The superiority of one breed or 
animal over another as regards feeding capacity is often as- 
cribed to a difference in the extent to which the feed is digested, 
although those who make this assertion often understand by 
digestion what is more properly termed " utilization." Un- 
doubtedly there are differences in digestive power between 
different animals, but except in the case of manifestly ab- 
normal animals they have been found to be comparatively 
slight and quite insufficient to account for the marked differ- 
ences in production (718, 719). Neither is there any evidence 
that the improved breeds of meat-producing animals possess 
any superiority in this respect over the ordinary unimproved 
animals. 

An illustration of the latter fact is afforded in experiments by 
Armsby and Fries, 1 in which no material difference was observed in 
the digestive powers of a pure-bred beef animal and a " scrub" at 
the approximate ages of one, two and three years. The same experi- 
ments also failed to show any material differences in the losses of 
energy in urine and methane, so that the percentage of the feed 
energy which was metabolizable, especially when computed on the 

1 U: S. Dept. of Agr., Bur. Anim. Indus., Bui. 128 (191 1). 



MEAT PRODUCTION 



441 



energy of the digested matter, was substantially the same for the two 
animals. The figures for the digestibility of the dry matter and for 
the percentage of the digestible energy metabolizable, each being the 
average of two periods, were as follows : — 

Table 116. — Digestibility by Pure-bred and Scrub Steers 





Timothy Hay 


Grains 




Steer A 
Pure-bred 


Steer B 
" Scrub" 


Steer A 
Pure-bred 


Steer B 
" Scrub" 


Digestibility of dry matter 
Experiment of 1905 .... 
Experiment of 1906 .... 
Experiment of 1907 .... 

Percentage of digested energy 

metabolizable 
Experiment of 1905 .... 
Experiment of 1906 . .• . . 
Experiment of 1907 .... 


% 

52.8 

53-7 
62.0 

79.91 
79.88 
78.75 


% 

54-9 

55-5 
61.4 

80.07 

79-57 
77.92 


% 
66.1 
81.4 
77-8 

81-53 
81.99 

81.73 


% 
66.5 
80.4 
78.8 

80.97 
81.41 
78.95 



516. Assimilative power. — This term may be used to 
designate broadly the ability of the organism to convert the 
digested nutrients of the feed into body tissue. Is the good 
meat producer able to form from a unit of digested feed of a 
given kind more new tissue than can the inferior animal ? In 
other words, is the net energy value of the feed affected by the 
individuality of the animal? As yet there has been scarcely 
any scientific investigation bearing upon this question, but 
such evidence as is available does not indicate the existence 
of material differences in this respect. 

Such of Kellner's determinations of net energy values for fatten- 
ing (449) as were made upon similar feeding stuffs with different 
animals show a generally good agreement as regards the utilization 
of the energy of the feed, although it does not appear from the ac- 
counts of the experiments whether or not the animals used differed 
materially in type. 

The experiments by Armsby and Fries, just referred to, were directed 
more specifically to the investigations of this question. They failed 
to demonstrate any decided advantage on the side of the pure-bred 



442 NUTRITION OF FARM ANIMALS 

animal so far as the percentage utilization of the energy supplied in 
excess of the maintenance requirement was concerned, the slight 
difference observed, especially in the earlier years, being perhaps 
accounted for by the greater tendency of the pure-bred steer to 
lay on fat. 

In the aggregate a considerable number of breed tests of cattle, 
sheep and swine have been made by the American experiment stations, 
the results of some of which have been summarized by Henry x so as 
to show the quantity of feed consumed per unit of gain. While in 
individual cases considerable fluctuations are to be found, neverthe- 
less, the results as a whole certainly fail to indicate any marked su- 
periority of one breed over another in this respect, and later experi- 
ments have not given materially different results. When we come to 
consider the other possible factors, such as differences in live weight, 
in maintenance requirement, in total feed consumed, etc., we must 
conclude that the recorded results give no clear evidence of any 
specific individual or breed differences in the actual physiological 
processes involved in the conversion of feed into tissue, although it is 
equally true, of course, that they fail to prove the absence of such 
differences. 

It seems clear that it is necessary to look elsewhere than to 
a supposed greater digestive and assimilative capacity of the 
typical meat-producing animal for an explanation of his eco- 
nomic superiority over the less specialized individual. 

517. The maintenance requirement. — It was shown in 
Chapter VIII (376, 391) that not inconsiderable differences 
may exist between different individuals as regards the main- 
tenance requirement. Thus in the case of cattle the extreme 
figures of 4.72 Therms and 7.43 Therms of net energy per 1000 
pounds live weight were observed for thin animals. Of the 
various factors affecting the maintenance requirement, it was 
pointed out that one of the most important is the degree of 
muscular activity of the animal even when in the state of so- 
called rest, and the decidedly lower maintenance requirement 
found by Armsby and Fries for a pure-bred beef steer as com- 
pared with a scrub was there interpreted as probably due to 
the more nervous disposition and greater restlessness of the 
latter. 

It is clear, however, that of two animals receiving identical 
rations the one which has the lower maintenance requirement 

1 Feeds and Feeding, 10th Ed., pp. 328 and 511. 



MEAT PRODUCTION 443 

will have the larger surplus for growth or fattening and, other 
things being equal, will make the greater increase per unit of 
total feed. To what extent a lower maintenance requirement 
is characteristic of high-bred meat-producing animals remains 
to be determined. If it appears to be a general fact, it would 
go far toward explaining any superiority on the part of the latter. 
It is not impossible, also, that differences in the amount of 
muscular activity may play a more important part in fattening 
than in the experiments on maintenance hitherto reported. In 
the latter, the experimental conditions necessitated consider- 
able restriction of the freedom of motion, while under the con- 
ditions of practice a wider scope may perhaps be afforded to 
the individuality of the animal in this respect. 

518. Feed consumption. — Another important element of 
individual superiority is the ability of an animal to consume 
regularly large amounts of feed. Of two animals otherwise 
similar, it is clear that the one which is able to consume day 
after day the heavier ration is the better meat producer. It is 
not always realized, however, that the heavier feeder makes a 
relatively more profitable use of his feed because, as pointed 
out in Chapter VIII (360), assuming the maintenance require- 
ment to be the same, the productive part of the ration forms a 
larger part of the total ration in the case of the large eater. 
Consequently, since all the feed must be paid for, this animal 
makes the more economical gain, not because he utilizes his 
excess feed better but simply because he is able to consume 
more of it. 

There are doubtless marked differences between individual 
animals in this respect. Whether the specific meat-producing 
breeds as a whole possess any advantage in this respect appears 
doubtful in view of the results on record regarding the feed cost 
of gain with different breeds. Apparently the quality is one 
to which the attention of breeders has not been specially di- 
rected, yet it is one which, it would seem, might well repay 
attention. 

519. Type and conformation. — It is a well-recognized fact 
that the conformation of a meat animal is a very important 
factor in determining his selling price. The improved meat 
breeds as a rule show a higher ratio of dressed to live weight, 
a better distribution of fat in the finished carcass, a somewhat 



444 NUTRITION OF FARM ANIMALS 

larger proportion of the higher priced cuts and a higher quality 
of meat. They are all important factors in the economic pro- 
duction of meat, but there is no evidence that their possession 
renders an animal any more efficient as a converter of feed into 
meat. 

520. Early maturity. — The economic importance of a rapid 
rate of growth and of the consequent early maturity has been 
considered in previous paragraphs (504, 505). 

It is a matter of common experience that there exist marked 
differences between individuals of the same species both as to 
the weight finally attained by the mature animal and as to the 
rate of growth at the same age. It is natural to interpret this 
fact as indicating corresponding individual differences in the 
rate of growth, especially of protein tissue, but the writer is 
not aware of any recorded experiments bearing specifically on 
this point. It is true that the quality of early maturity is 
popularly attributed to the meat breeds, but as regards cattle 
at least Henry l has shown that the data at hand fail to prove 
that the beef breeds as such show a greater rate of gain in live 
weight or a greater weight at maturity than do the dairy breeds, 
although it is likewise true that other elements than simply 
the weight enter into the economic conception of maturity. 
If it is correct to ascribe the individual differences noted above 
to variations in the rate of growth of protein tissue, it sug- 
gests a field for investigation of much interest both to the 
breeder and the feeder. 

§ 3. Feeding for Meat Production 

521. Feeding as related to individuality. — The facts consid- 
ered in the previous section relate to the capacity of the animal 
as a mechanism for the conversion of vegetable products into 
meat. They (and other less important ones) determine the 
degree to which, from the commercial standpoint, the animal 
is able to utilize the feed given it. Favorable modifications 
of any of these factors are of advantage because they enable a 
larger and more profitable production to be secured. 

Feeding stands in a somewhat different relation, in that its 
purpose is to supply the material upon which the mechanism 

1 Feeds and Feeding, 10th Ed., p. 329. 



MEAT PRODUCTION 445 

works. It is of prime importance to the feeder that his animals 
shall have the largest possible productive capacity, but while 
the maximum which the animal can produce is determined by 
its breed and individual characteristics and cannot be materially 
affected by feeding, the amount which it actually does produce 
in any given case must depend upon the amount of material 
supplied to it in its feed. Production may be limited by a 
deficient feed supply, although it cannot be forced above a cer- 
tain maximum by increasing the ration. 

522. Feed requirements. — Since feed is to be looked upon 
as a supply of raw material for the animal mechanism, it is clear 
that the kind and amount required will depend primarily upon 
the capacity of the animal. The young animal, with his marked 
capacity for growth, will require relatively more of the specific 
materials for growth, viz., protein and ash, than will the older 
animal. The early maturing animal, with his greater rate of 
growth, will require more total feed per day than the one ma- 
turing more slowly. The animal with the capacity to con- 
sume and utilize large total amounts of feed must be given these 
larger amounts in order that his advantage in this respect 
may be fully utilized. 

As already pointed out, meat production is a combination of 
growth and fattening, the latter process being superimposed 
upon the former. The feed requirements of the meat-producing 
animal, therefore, include in the first place the requirements for 
normal growth, to which are added during a longer or shorter 
time according to circumstances the requirements for the pro- 
duction of fat. The feed requirements for these two purposes 
have already been considered in the two previous chapters, but 
may be conveniently recapitulated here with more particular 
emphasis on economic relations. 

Protein requirements for meat production 

523. Relation to age. — It was shown in Chapters X and XI 
that it is only during growth that any considerable production 
of meat in the narrower sense, i.e., of muscular tissue, takes 
place, and likewise that the energy of growth is greatest in the 
young animal and diminishes, at first rapidly and then more 
and more slowly, until physiological maturity, when but a slight 



446 NUTRITION OF FARM ANIMALS 

increase of the total protein and still less of meat proper can be 
secured. Evidently the question of the necessary protein supply 
in the rations of meat-producing animals is of special impor- 
tance during the early stages of growth. 

524. Minimum protein supply for growth. — The meat-pro- 
ducing animal, then, in order to utilize fully his capacity for 
growth must be supplied in his feed at each stage of that growth, 
in addition to his maintenance requirement, with at least as 
much digestible protein as he is capable of storing up in his 
growth. Whether any greater quantity than this is necessary 
or advantageous is, as has been shown (491), still to some de- 
gree an unsettled question. Some experiments, especially with 
cattle and sheep, indicate that any considerable surplus is un- 
necessary for normal growth, while, on the other hand, feeding 
experiments with pigs and to some extent with ruminants indi- 
cate that amounts considerably in excess of those thus com- 
puted assure at least greater gains of live weight. 

525. Protein requirements in fattening. — While growth 
and fattening may be regarded physiologically as distinct pro- 
cesses, it is economically important in the practice of meat pro- 
duction that they should go on more or less simultaneously. 
The growth of even the very young animal is not simply a 
production of protein tissue, but normally includes more or less 
fat production, while in proportion as one has to deal with 
early maturing animals it is desirable to begin the fattening 
proper at a comparatively early stage of growth (512) . 

There appears to be no reason for regarding the actual fatten- 
ing process as being essentially different in the growing and 
in the mature animal. It has been shown, however (453, 456) 
that in the latter case no material excess of protein over that 
required for maintenance is necessary. So far as the mere 
supply of building materials is concerned, therefore, there seems 
no reason to suppose that the actual protein requirement for 
combined growth and fattening is any greater than that for 
normal growth without fattening. The conclusions regarding 
the protein requirements for growth recorded in Chapter XI 
(482), therefore, may be regarded as applicable also to young 
animals that are being fattened, especially since they were de- 
rived in part from results on immature fattening animals, and 
from this point of view the increased feed supply required for 



MEAT PRODUCTION 447 

the fattening might consist exclusively of non-nitrogenous 
nutrients. 

526. Influence on digestibility. — In the actual compound- 
ing of rations for fattening, however, whether for mature or for 
growing animals, account must be taken of the fact that such 
a considerable addition of non-nitrogenous nutrients to a 
maintenance or growth ration may have an unfavorable effect 
upon its digestibility. In particular, it has been shown (723) 
that a large proportion of easily digestible carbohydrates in a 
ration (i.e., a " wide " nutritive ratio) tends to depress the 
apparent digestibility of the protein. Accordingly, if, starting 
with a ration just adequate to support the normal rate of growth, 
the attempt be made to convert it into a fattening ration by 
simply increasing its digestible carbohydrates, the effect may be 
to virtually diminish the amount of protein available so that 
the ration, while containing abundant material for fat produc- 
tion, may fail to supply enough protein to utilize fully the 
animal's capacity for growth. 

The increase due to growth, however, is an important factor 
of the cheaper gains made by immature animals (509). In in- 
creasing the total feed supply in order to secure the fattening 
of the young animal, therefore, it is important to avoid the dan- 
ger of so decreasing the apparent digestibility of the protein 
by the too free use of feeding stuffs rich in carbohydrates as to 
reduce the protein supply below that needed for growth. More- 
over, it has been found (723-727) that a relative deficiency of ni- 
trogenous matter in a ration also decreases the digestibility 
of the carbohydrates, particularly of those less soluble forms 
which are acted upon chiefly by the fermentative processes in 
the rumen or ccecum, and so tends to reduce the energy value 
of the ration. 

It is difficult, however, to make any very definite statements 
regarding the practical significance of these effects in actual 
feeding. Kellner recommends that the nutritive ratio (709) of a 
fattening ration, computed in the usual way, be not made wider 
than about 1:8-9 f° r cattle and sheep and 1:10-12 for 
swine. Ordinarily, there will be little difficulty in compound- 
ing rations conforming to this rule, especially when home grown 
protein feeds are available, and such rations when fed in suf- 
ficient amounts to support reasonably rapid fattening would 



448 NUTRITION OF FARM ANIMALS 

supply more digestible protein than is called for by the estimates 
in Appendix Table IV b. When protein feeds are especially ex- 
pensive an even smaller proportion of protein might doubtless 
be used to economic advantage, even though at the expense of 
some loss of digestibility, without unduly curtailing the pro- 
tein supply, especially in the case of animals approaching 
maturity. 

527. Specific effects of feeding stuffs. — Account must be 
taken also of the fact that in most of the experiments upon the 
protein requirement thus far reported the variation in the 
protein supply was effected by varying the proportions of cer- 
tain concentrates in the ration, such, e.g., as substituting cotton- 
seed meal for maize. As was suggested in Chapter XI (491), 
however, such a substitution may not only affect the ash bal- 
ance of the ration but may serve to introduce substances which 
stimulate the growth process or perhaps the fattening process. 
While we are not to suppose that such substances can take 
the place of actual nutrients (738), they might enable the 
protein in the ration to be more fully utilized, or they might, 
by stimulating the fattening process, create an appetite for more 
feed. 

At any rate it seems to be the general experience of stockmen 
that the addition of certain feeds rich in protein, especially the 
oil meals, to the rations of fattening animals tends to induce 
them to consume feed more freely and thus (518) to yield more 
profitable gains. 

Energy requirements for meat production 

528. Combined growth and fattening. — An attempt was 
made in Chapter XI (480-483) to estimate approximately the 
net energy values required at different ages for normal growth 
without material fattening. To the extent to which the fatten- 
ing process is to be carried on at the same time, these require- 
ments must evidently be increased by amounts equal to the 
additional net energy stored up in the increase of adipose tis- 
sue desired or expected. Subject to the limitations indicated 
in previous paragraphs, this additional energy may be supplied 
by the addition of either nitrogenous or non-nitrogenous ma- 
terials to the growth ration. 



MEAT PRODUCTION 449 

It was estimated in Chapter X that a pound of increase in 
live weight in the mature fattening animal is equivalent to about 
3.25 Therms of energy. If it is allowable to apply this average 
to the fattening of younger animals, this would be equivalent 
to saying that for each pound of increase in weight above that 
due to growth proper, about 3.25 Therms of net energy should 
be added to the requirements for growth as estimated in Chapter 
XI (480-483). The energy requirement of the meat animal, 
therefore, will obviously depend on its capacity to produce gain 
of flesh or fat and the extent to which it is desired to utilize this 
capacity, and no specific and invariable requirements can be 
formulated. 

529. Total amount of feed. — If, for the reasons given in 
previous paragraphs, the proportion of digestible protein in the 
ration is kept above a certain limit, the question of the amount 
of net energy to be supplied resolves itself into the question of 
the most profitable total amount of feed to be given and this 
depends upon a variety of conditions. 

It has already been pointed out (512) that only with animals 
having a rapid rate of growth and maturing early is it advisable 
to begin intensive feeding before a fair degree of maturity is 
reached. With ordinary animals the major portion of their 
growth may be more cheaply supported upon pasture and the 
ordinary roughages with relatively small amounts of concen- 
trates, since the growth process cannot be materially has- 
tened by heavy feeding. When, however, the time for begin- 
ning the fattening process involving the use of expensive con- 
centrates is reached (533), whether this be early or late, it is 
important to hasten it as much as practicable in order to re- 
duce the cost of maintenance, attendance, etc., and the question 
of the most profitable amount of feed becomes an important one. 

530. Heavy feeding profitable. — That comparatively heavy 
feeding of fattening animals is economically advantageous is 
shown by the experience of practical feeders, and is evident from 
the fact, to which attention has already been called several times, 
that a less proportion of the heavy ration is required for the 
maintenance of the animal. Were this the only factor involved, 
it would follow mathematically that the greater the amount of 
feed consumed the greater would be the growth per unit of feed 
and therefore that the appetite of the fattening animal should 

2 G 



450 NUTRITION OF FARM ANIMALS 

be stimulated to the greatest extent possible. In fact, how- 
ever, other considerations come in to modify this conclusion. 

531. Influence on digestibility. — Overfeeding to the ex- 
tent of causing digestive disturbances and throwing the animal 
" off feed " is of course to be avoided, since the resulting dis- 
turbance and the subsequent lessened consumption of feed 
may outweigh any advantage from the increased amount eaten. 
It is the regular uniform feeder that is likely to be the profitable 
animal rather than the one with a capricious appetite. 

But aside from this danger, it seems well established that 
the percentage digestibility of mixed rations, such as would be 
used in productive feeding, decreases more or less as the quantity 
consumed increases. The results on record in this respect (722) 
are scarcely sufficient for any quantitative estimate of the mag- 
nitude of this effect, but it is evident that it must tend to di- 
minish the efficiency of the rations. 

532. Influence on net energy values. — Such a decrease of 
digestibility as that just noted is, of course, equivalent to a 
decrease in the net energy value of the rations. There appears 
to be a somewhat general impression, however, that in addition 
to this effect on digestibility, the matter and energy actually 
resorbed from the ration become less efficient in producing 
gain as the amount of the ration is increased — in other words 
that when the organism is flooded with the resorbed products 
of digestion, the katabolic processes are stimulated and a larger 
share of the energy of the digested matter escapes as heat. • 
As appears in Chapter XVII (764), the evidence on this point 
as yet seems hardly sufficient to warrant positive statements. 
The net energy values of feeding stuffs which have thus far been 
reported have been obtained chiefly in experiments on rations 
ranging from submaintenance to only moderately heavy fatten- 
ing rations, and the results show no distinct indication of a 
decrease with increasing amounts of feed. On the other hand, 
physiological considerations render it quite conceivable that 
the effect of the feed in stimulating metabolism and so increasing 
the heat production (365) may be relatively greater on a high 
than on a low nutritive plane. 

Apparently more or less falling off in the nutritive effect of 
a fattening ration as its amount is increased must be antici- 
pated, whether on account of decreasing digestibility or of 



MEAT PRODUCTION 451 

lessened utilization of the digestible matter or a combination 
of the two. Whether this diminution, within the limits of the 
animal's capacity to consume feed, is sufficient to offset the 
economic advantage of such increased consumption remains to 
be shown, although Morgen * reports experiments on sheep in 
which very heavy rations, actually produced smaller gains in 
live weight than lighter ones. Finally it should be remembered 
that it is the actual gain of chemical energy by the animal which 
is believed to bear a tolerably constant relation to the feed en- 
ergy. It has been repeatedly pointed out that the gain in live 
weight is a very uncertain indication of the amount of energy 
stored up. It is quite conceivable that the larger gain to be 
expected on the heavier ration may contain less water and more 
dry matter or less protein and more fat than that produced on 
the lighter ration, and that consequently the increase in weight 
may not be proportional to the increase in feed. In that case, 
unless the higher quality of the gain were recognized by the 
market, the economic advantage attached to heavier feeding 
would be diminished or wiped out. 

533. Proportion of concentrates to roughage. — The fore- 
going considerations apply in the first instance to varying 
amounts of the same mixture of feeding stuffs. In the case of 
herbivora, however, heavy feeding must necessarily be effected 
by increasing the proportion of concentrates or of roots to 
roughage, the higher cost of the former per unit of net energy 
being more than offset by the economic advantage incident to 
the much larger amount which can be consumed. When such 
an addition of concentrates contains a large proportion of 
carbohydrates (as in the case of maize or roots) it would appear 
(724) that the digestibility of the rations would suffer to a certain 
extent owing to the low protein content of the ration, while 
common observation indicates a more rapid passage of the 
feed through the digestive tract of heavily grained ruminants 
and suggests a decrease in total digestibility which has not, 
however, been experimentally confirmed. 

534. Standards. — It is clear from the foregoing that under 
ordinary conditions mature or nearly mature fattening animals, 
such as the cattle ordinarily fattened in the United States, 
should be fed as heavily and pushed as rapidly as the capacity 

1 Futterung unci Schlachtergebnisse, pp. 22 and 33. 



45 2 



NUTRITION OF FARM ANIMALS 



of the animals and the skill of the feeder will permit. This 
conclusion was reached long ago by practical feeders, so that the 
results of experience and of investigation appear quite in har- 
mony. Such an intensive feeding can be effected only by a 
free use of concentrates and unless the latter are very expensive 
as compared with roughages, it is economy to use them to the 
largest practicable extent. 

Under these conditions it is evident that there is very little 
significance in a feeding standard in the ordinary sense, so far 
at least as the amount of feed is concerned. It may, it is true, 
afford a basis for preliminary computation of the amount 
of feed required for a season's feeding, if this is of any impor- 
tance, but in actual feeding the problem is to induce the animals, 
by means of the art of the skilled feeder, to consume large 
amounts of feed without injury to their appetites or digestive 
capacity, and this is largely a question of the individuality of 
the animal or lot. The one thing to be kept in mind is to see 
that the supply of protein in the ration is sufficient to ensure the 
normal growth of protein tissue, since this causes a relatively 
rapid increase in weight. 

For younger fattening animals, somewhat more definite re- 
quirements might be formulated in the manner indicated in a 
previous paragraph (528) on the basis of the requirements for 
fattening and for growth as estimated in Chapters X and XL 

The compilation by Bull and Emmett l of American experi- 
ments on fattening lambs referred to in Chapter XI (487) in- 
cluded data regarding the computed net energy content of the 
rations. They conclude that the production of satisfactory 
gains required the following amounts of digestible protein and 
net energy per iooo pounds live weight. 

Table 117. — Requirements of Fattening Lambs per iooo Lb. Live 

Weight 



Live Weight 


Estimated Age 


Digestible Protein 


Net Energy 


Pounds 


Months 


Pounds 


Therms 


50-70 


5 


3-1-3-3 


17-19 


70-90 


7 


2.5-2.8 


18-20 


90-110 


9 


2.2-2.4 


17-20 


110-150 


15 


1.4-1.9 


16-19 



1 Ills. Expt. Sta., Bui. 166 (1914). 



MEAT PRODUCTION 453 

No similar compilations for other species of farm animals have 
yet been reported, although much valuable material in the 
publications of the experiment stations awaits such discussion. 

§ 4. Influence of External Conditions 

While the capacity of the animal as a meat producer and a 
supply of feed sufficient in quantity and quality to fully utilize 
that capacity are the two great factors in meat production, yet 
the conditions under which the animal is kept are not without 
influence on the results obtained. 

Temperature 

535. Teachings of practice. — Since the temperature of the 
animal body is maintained by the katabolism of materials de- 
rived from the feed, it seemed natural to conclude that cold 
surroundings would lead to a wasteful oxidation of feed for 
simple heat production, and considerable emphasis has been 
laid in the past upon the economic importance of providing 
fairly warm quarters for live stock. At the same time, however, 
great numbers of cattle, in particular, were being successfully 
fattened in sheds and open feed lots and more recently a con- 
siderable amount of experimental work has been reported show- 
ing that this supposedly uneconomic practice actually gives 
better returns than feeding in warm quarters. The results of 
a considerable number of such comparisons have been sum- 
marized by the writer l and leave no doubt as to the validity 
of this conclusion, while it is entirely in harmony with the prin- 
ciples governing the influence of external temperature upon 
metabolism which were discussed in previous chapters. 

536. Critical temperature. — As was shown in Chapter VII 
(354), there is a certain approximate temperature, called the 
critical temperature, at which the minimum outflow of heat 
just balances the necessary heat production resulting from the 
internal work and below which more or less oxidation of tissue 
is required to maintain the normal temperature of the body. 
Furthermore, it has been shown (395-397) that the digestion 
and assimilation of feed and its conversion into tissue result in 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 108 (1908), pp. 79-86. 



454 NUTRITION OF FARM ANIMALS 

the evolution of relatively large amounts of heat, especially 
in the ruminants, and that the effect of this internal produc- 
tion of heat is virtually to lower the critical temperature as com- 
pared with that of the fasting animal. In other words, there is 
for each animal and for each ration a certain temperature above 
which the heat produced becomes in part an excretum, to be 
gotten rid of by radiation and evaporation. 

It appears likely that a certain excess of heat production over 
that absolutely required to maintain the body temperature is 
advantageous, both as promoting the comfort of the animal and 
especially as affording a margin in case of temporary fluctuations 
of temperature. On the other hand, both our own personal sen- 
sations and the observations of practical stock feeders show that 
an unnecessarily high temperature is debilitating, affecting both 
appetite and general health. In practice, then, it is desirable to 
keep the thermal surroundings of the animal within the range 
above indicated — somewhat above the critical point but not 
so much so as to affect the appetite and thrift. It is evident 
that the limits of this range may vary widely with the kind of 
animal and with the amount of the ration. 

537. Amount of ration. — The influence of this factor upon 
the requirements for protection from cold is clearly indicated 
by what has already been said. The heavier the ration, other 
things being equal, the more heat will be evolved during its 
digestion and conversion into tissue. Mature animals on full 
feed thus have at their disposal a large amount of surplus heat 
and naturally can thrive under conditions of exposure which 
might be seriously detrimental to young, growing animals on 
relatively light rations. Thus one of Kellner's experiments on 
a fattening ox gave the following results : — 

Table 118. — Excess Heat Production in Fattening 

Metabolizable energy of ration 26,600 Cals. 

Energy stored as gain 5>92o Cals. 

Energy evolved as heat 20,740 Cals. 

Computed maintenance requirement .... 15,060 Cals. 

Excess of heat 5, 680 Cals. 

Excess over maintenance 37-7% 

538. Age and weight of animals. — The internal work of 
like animals of different sizes, under like conditions, appears to 



MEAT PRODUCTION 455 

be approximately proportional to their body surface (345), 
and there is even good ground for believing that this law applies 
in a broad way to animals of the most diverse species and size. 
Since the action of external temperature is also approximately 
proportional to the surface, it would be expected that the size 
of the animal would not be an important factor. In fact, however, 
the other conditions are rarely alike. The young animal in 
particular is likely to be getting a relatively lighter ration than 
the animal which is being pushed for the butcher, and thus to 
have less surplus heat at its disposal, while the indefinable factor 
of " hardiness " would also seem to be in favor of the older 
animal. 

539. Humidity. — The relative humidity of the air is an im- 
portant factor in the temperature relations of the animal. 
Moist air tends to increase the conductivity of the hair or wool, 
just as it does that of the clothing of man, thus facilitating the 
escape of heat and raising the critical temperature. Accord- 
ingly, it is to be anticipated that in a dry climate, like that of 
the northwestern United States, animals might be safely exposed 
to a greater degree of cold than in a damp climate, like the 
winter of the seaboard States. 

540. Temperature of drinking water. — In general, the 
same considerations adduced in discussing the influence of the 
temperature of the air apply to that of the drinking water. 
Under heavy feeding, especially, unless in very cold quarters, 
the animal has a surplus of heat which it can apply to warming 
its drink. If, then, the latter is at such a temperature as to be 
consumed freely, there would seem to be no occasion for heating 
it further, except for one important consideration. The tem- 
perature of the air acts continuously and with approximate 
uniformity. That of the water, on the other hand, acts only 
at intervals, often only two or three times or even once per day. 
If, now, the animal consumes within a short time a large amount 
of cold water, a correspondingly rapid expenditure of heat is 
required to warm this water to the body temperature, and this 
demand may for a time exceed the supply of surplus heat and 
cause an increased oxidation of tissue or food material for the 
sake of heat production only. Such a loss can never be made 
good at a later hour since, once converted into heat, the energy 
has escaped from the grasp of the body. Other things being 



456 NUTRITION OF FARM ANIMALS 

equal, then, it will clearly be desirable to have the water con- 
sumption approximate as nearly as possible a continuous con- 
sumption by having it constantly accessible, while if the stock 
are watered only at intervals the temperature of the water may 
need to be rather higher than in the other case. 

Shelter 

A protection from rain or snow and from wind may be of quite 
as much importance as protection from low temperatures simply. 

541. Precipitation. — An important factor in the case is 
the amount of precipitation (rain or snow) to be expected dur- 
ing the feeding period. In cold weather the low temperature 
of the water which penetrates to the skin of animals is the cause 
of a loss of heat which may be regarded as practically an ad- 
dition to that due to the cold air, the extent of both losses being 
affected by the thickness of the animal's coat. Far more im- 
portant than this, however, is the expenditure of heat re- 
quired to dry out the coat after it is wet, and this, as it would 
seem and as some of the experiments with sheep seem to indi- 
cate, would be greater with the heavier coated animal when it 
has once become thoroughly wet. Still greater, relatively, is 
the heat required to melt the snow falling on the animal or that 
upon which it is compelled to lie. 

These effects, it will be observed, are largely independent of 
the indications of the thermometer, and it is clear that the 
nature of the climate as regards humidity and precipitation is 
quite as important a factor as the temperature in its bearing 
on the question of shelter, and that in many localities a roof to 
shelter the animals from storms may be as efficient as a tight 
barn. One • advantage of the roof, already mentioned inci- 
dentally, is that it provides the possibility of a dry bed, thus 
not only adding to the comfort of the stock but avoiding ex- 
penditure of energy in warming up or evaporating water or melt- 
ing snow or ice. 

542. Wind. — All are familiar with the greater severity of a 
windy day as compared with a still one of the same temperature. 
A large part of the protective value of the clothing of man or 
the coat of an animal resides in the air entangled between the 
fibers of the material. Wind tends to replace this air with fresh, 



MEAT PRODUCTION 



457 



cold air and thus greatly reduces the protective effect. A wind- 
break, therefore, may have a distinct economic value in stock 
feeding. 

543. Insolation. — The effects of the weather are appreciably 
modified by the exposure of stock to direct sunlight. Aside from 
any direct effect of the light as such, a not inconsiderable amount 
of heat is imparted to the body by the sun's rays. During cold 
weather this is likely to be a distinct advantage, but during the 
hot months the reverse is true. Since the animal cannot re- 
duce its heat production below that resulting from its internal 
work and the digestion and assimilation of its feed, it may se- 
riously tax its powers to dispose of the additional heat imparted 
by the direct sunlight. In this case shelter of some sort may 
be required for opposite reasons to those obtaining during the 
cold months. For similar reasons a supply of cool, fresh water 
and exposure to the wind may be of great advantage in helping 
the animal to get rid of its surplus heat. 

Other conditions 

^ 644. Exercise. — The well-known fact that muscular exer- 
tion is accomplished at the expense of the katabolism of tissue 
and ultimately, therefore, at the expense of the feed, would seem 
at first thought to indicate that the activity of the meat-produc- 
ing animal should be restricted as much as practicable. In the 
case of the growing animal, however, another very important 
element enters into the case, namely, the fact that moderate 
exercise tends to stimulate the growth of the muscular system, 
or, in other words, the production of lean meat. Since this is 
the essential object sought, a normal and reasonable amount of 
muscular activity on the part of the growing animal should be 
allowed and encouraged, even though the muscular exercise 
involves the consumption of more feed. Accordingly, young 
stock should be given the freedom of the pasture or range to 
as great an extent as practicable, while at the same time care 
should be taken to supply abundant feed containing a sufficient 
supply of protein in order that enough material may be present 
to supply the demand for growth stimulated by the exercise. 

In the case of breeding stock, especially, a most important 
consideration is that of the health and stamina of the animal, 



458 NUTRITION OF FARM ANIMALS 

which can hardly fail to suffer through overconfinement. The 
above principles apply in a general way to all classes of stock. 
In particular, hogs should be given an opportunity for more 
movement and exercise than is frequently allowed. 

In the case of animals which have reached the fattening stage, 
on the other hand, there is comparatively little growth of pro- 
tein tissue, while it is only necessary to maintain sufficient health 
to ensure a normal appetite and assimilation of feed. In pro- 
portion, then, as this stage is reached, the endeavor should be 
to reduce the amount of exercise taken and to keep the fatten- 
ing animal as quiet as possible. To this end comfortable quar- 
ters should be provided, with plentiful bedding, and the animals 
should be kept as undisturbed as possible, so that they may 
" eat and lie down." This is particularly important in the case 
of the sheep on account of its timid nature. For similar rea- 
sons it is desirable to have the water supply of fattening animals 
close at hand. 

545. Water supply. — It should never be forgotten that 
rapid production, involving the utilization of relatively large 
amounts of feed, requires the consumption of a corresponding 
amount of water for the physiological purposes of the animal. 
For this reason, as well as for the one previously mentioned (540) , 
it is desirable that stock should have ready access to water, if 
possible, at all times and that the water supplied should not be 
too cold to be consumed freely by the animals. 






CHAPTER XIII 
MILK PRODUCTION 

§ i. The Physiology of Milk Production 

546. Components of milk. — In addition to water, milk 
contains representatives of the four great groups of nutrients, 
viz., proteins, fats, carbohydrates and ash. 

Proteins. — The principal protein of milk is casein, a sub- 
stance belonging to the group of phosphoproteins (55). This 
protein is peculiar to milk, not being found elsewhere in the 
body. 

In addition to casein, milk contains also a lact-albumin and a 
paraglobulin in small amounts. Their presence may be demon- 
strated by precipitating the casein by means of acid and heating 
the filtrate. Traces of peptones, possibly due to the presence 
of a proteolytic enzym, are also found in milk. 

According to Konig, the casein content of milk has been 
observed to vary from 1.79 per cent to 4.23 per cent and that 
of the other proteins from 0.25 per cent to 1.44 per cent. 

Fats. — Fats occur in milk in the form of microscopic glob- 
ules varying greatly in size and held in suspension in the col- 
loidal solution of casein. In cow's milk the diameter of these 
fat globules may be stated in a general way to range from 
0.0016 to 0.01 millimeter and in a single cubic centimeter of 
average milk their number runs into the millions. The fat 
globules were formerly described as surrounded by a membrane 
of a protein nature, but the supposed membrane is now re- 
garded as simply a condensation of the protein of the milk, due 
to surface tension. 

Milk fat, like other animal fats, is a mixture of a number of 
simple fats or triglycerids. As compared with body fats, the 
fat of milk is relatively rich in olein and consequently has a 
relatively low melting point. It is especially distinguished from 

459 



460 NUTRITION OF FARM ANIMALS 

body fat, however, by the presence of a considerable proportion 
of fatty acids of low molecular weight, as already noted in 
Chapter I (30), where a list of the principal constituents is 
given. The presence of these so-called " volatile fatty acids " 
(i.e., acids which can be distilled in a current of steam) affords 
an important means for the detection of adulterations of 
butter. 

The percentage of fat in milk varies widely. For the cow a 
minimum of 1.67 per cent is reported by Konig. Six per cent, 
on the other hand, is a high figure, although occasionally 7 per 
cent is reached. Babcock states that 9 per cent is the maxi- 
mum observed for a cow giving as much as 15 pounds of milk 
daily. 

The milk fat carries traces of lecithins and cholesterins 
and also varying amounts of coloring matter, derived, as 
Palmer and Eckles * have shown, chiefly from the carotin of 
the feed. 

Carbohydrates. — Milk contains in solution a disaccharid 
peculiar to itself, namely, lactose, or milk sugar (13). In 
distinction from fat, the percentage of lactose in fresh milk 
shows comparatively small variations, averaging about 5 per 
cent in cow's milk. The souring of milk is brought about by a 
fermentation of the milk sugar by which its molecule is split 
into four molecules of lactic acid. 

Among the organic ingredients of milk should also be men- 
tioned citric acid, which occurs in appreciable quantities in the 
form of calcium citrate. 

Ash. — The total mineral matter in cow's milk averages 
about 0.7 per cent according to Van Slyke. 2 

Qualitatively, the ash of milk contains the same ingredients found 
in all animal substances. Its quantitative composition, however, as 
compared with the blood serum, on the one hand, and with that of 
the tissues on the other, shows some interesting relations. Bunge 3 
gives the following figures for the composition of the ash of the serum 
of cattle blood and of the ash of cow's milk. To these have been 
added Lawes and Gilbert's figures for the ash of a calf for the sake 
of comparison. 

1 Jour. Biol. Chem., 17 (1914), 191-264. 

2 Jordan, The Feeding of Animals, 1908, p. 305. 
3 Ztschr. Biol., 10 (1874), 301 ; 12 (1876), 191. 



MILK PRODUCTION 
Table 119. — Percentage Composition of Ash 



461 



K 2 

Na 2 

CaO 

MgO 

Fe 2 3 

CI . 

P2O5 



Serum of 
Cattle 
Blood 



% 
3-2 

55-i 
1.6 
0.6 
0.1 

47.1 
3-4 



Cow's 
Milk 



Bodv OF 
Calf 



% 
22.1 

13-9 

20.0 

2.6 

0.04 

21.3 

24.8 



% 

5 -40 
3.82 

43-95 
2.20 

0-53 
0.12 

40.37 



With smaller animals, having a shorter period of growth, the rela- 
tions are even more striking. Thus, for the rabbit Bunge l reports 
the following results. 

Table 120. — Percentage Composition of Ash 



K 2 

Na 2 

CaO 

MgO 

Fe 2 3 

CI . 

P 2 5 



Serum of 
Rabbit 
Blood 



3-2 

54-7 
1.4 
0.6 
0.0 

47-8 
3-o 



Rabbit 
Milk 


10. 1 


7-9 


35-7 


2.2 


0.1 


5-4 


39-9 



Body of 
14 Days 

Old 
Rabbit 



10.8 
6.0 

35-0 
2.2 
0.2 
4.9 

41.9 



It appears that while sodium and chlorin are the predominant 
ingredients of the blood serum, these elements are present in milk in 
relatively small proportions, while potassium, calcium and phos- 
phorus predominate in the latter, the ash of milk closely resembling 
that of the body of the same species. 

547. Average composition. — Wing 2 cites the following 
figures as showing approximately the average composition of 
cow's milk 3 according to various authorities. 

1 Quoted by Sellheim in Nagel's Handbuch fiir Physiologie, II, 188. 

2 Milk and its Products, 1897, p. 17. 

3 For data regarding the composition of the milk of other species than cattle, 
see Schaefer's Text Book of Physiology, Vol. I, p. 125. 



462 NUTRITION OF FARM ANIMALS 

Table 121. — Average Composition of Cow's Milk 



Water . 
Fat . . 
Casein . 
Albumin 
Sugar . 
Ash . 



American 
(Babcock) 



87.17 
3-69 
3.02 

°-53 
4.88 
0.71 



100.00 



English 
(Oliver) 



87.60 

3-25 
3-40 
0-45 
4-55 
o.75 



100.00 



German 

(Fleisch- 

mann) 



87-75 
3-40 
2.80 
O.70 
4.60 
o.75 



IOO.OO 



French 
(Cornevin) 



87-75 
3-30 
3.00 

4.80 
°-75 



99.60 




548. Milk glands. — The milk glands, properly speaking, 
are two in number, one on each side of the median line of the 
body, although in many animals each gland is subdivided into 

two or more lobes having separate outlets 
or teats. Thus in the horse and sheep 
each gland has two lobes, in the cow 
two or three, and in the hog from ten to 
fourteen. The milk gland is classified 
as a compound tubulo-acinous gland. Its 
structure may be roughly compared to 
that of a bunch of grapes. It consists 
of a great number of acini or alveoli, 
three of which are shown schematically 
in Fig. 40, corresponding to the single 
berries of the grape cluster. Each alve- 
olus consists of an outer layer of con- 
nective tissue carrying capillary blood vessels, nerves and 
lymphatics. These alveoli are about -^ of an inch in diameter 
and are united in groups of 3 to 5 to form lobules having 
a common outlet as shown in the figure. Internally, the 
alveoli are lined with a single layer of epithelial cells (Fig. 41), 
which are the "active agents in secreting milk. The .ducts or 
passages leading from the alveoli are also lined with epithelial 
cells but of a different sort and which do not produce milk. 
These ducts unite to form larger ones, as shown in Fig. 42, which 
lead finally to the teat, emptying first into the so-called " milk 
cistern," a cavity lying near the base of the teat. In compound 



Fig. 40. — Lobule of milk 
gland. (Armsby, Manual 
of Cattle Feeding.) 



MILK PRODUCTION 



463 



milk glands there is more or less connection through these 
milk ducts between the several lobes, but none between the 
two glands on either side of the body. 
The milk gland, therefore, consists 
of a framework of connective tissue 
carrying more or less fat, of alveoli, 
milk ducts, veins, arteries, lymph vessels 
and nerves, the whole forming a reddish 
gray spongy mass. In the cow the 
two glands constituting the udder are 
separated by a band of fibrous tissue 
which serves to support the organ. 
The udder may vary widely in the 
proportion of connective and fatty 
tissue on the one hand and of true 
secreting tissue (alveoli) on the other. J^ YwiTck^ns^FormTnd 

A large proportion of the former gives Leben der Landwirthschaft- 

what is commonly known as a fleshy Uchen Haustmere -) 
udder. The size of the udder, therefore, is not the sole criterion 

of its capacity as a milk pro- 




*<¥>. 




ducing organ. 

At the branches of the milk 
ducts are located sphincter 
muscles which are more or less 
under the control of the animal 
and the contraction of which 
interferes with the flow of 
milk, enabling the animal, as 
the phrase goes, to " hold up " 
her milk. 

549. Development of milk 
glands. — In the young animal, 
the milk glands are rudimen- 
tary and in the male remain so 
during life, except in extraor- 
dinary cases. In the female, 
however, as sexual maturity 
approaches, a considerable 

*ig. 42. — Structure of milk gland. , ,. . , , , 

Vilckens, Form und Leben der Land- formation of glandular tissue 

takes place, but the glands 



(Wilckens, Form und Leben der Land 
wirthschaftlichen Hausthiere.) 



464 NUTRITION OF FARM ANIMALS 

reach their full 'development only in the later stages of preg- 
nancy. At that time, a rapid growth of the alveoli and per- 
haps the formation of new ones occurs, the stimulus to this 
growth being, according to Bayliss and Starling, the formation 
of certain stimulating substances (Hormones) in the fetus which 
pass into the blood of the mother and so reach the milk glands. 
That other causes may at least cooperate, however, is shown 
by the apparently well-established fact that the regular re- 
moval of the fluid found in the glands of the virgin animal, 
or even mechanical stimulation, may lead to the formation 
of considerable quantities of milk, in some instances even in 
the male. 

550. The secretion of milk. — That milk formation is a true 
secretion and not a mere filtration of material from the blood 
is clearly shown by the facts already stated regarding the com- 
position of milk. As was pointed out, all the principal organic 
ingredients of the milk are peculiar to it. Casein and lactose 
are not found elsewhere in the animal body, and while the prin- 
cipal simple fats of milk are also found in the body fat, their 
proportions are different in the milk fat and the latter is specially 
characterized by the presence of glycerids of the lower acids 
of the aliphatic series. Furthermore, even more marked quan- 
titative differences exist between the mineral elements of the 
milk and those of the blood serum. From all these facts, it is 
clear that the milk gland is a producing or secreting organ and 
that the solid ingredients of the milk are largely manufactured 
in it out of materials derived from the blood. 

A theory of milk secretion first propounded by Virchow 
found wide acceptance. According to this theory, milk pro- 
duction consists essentially of a physiological fatty degeneration 
of the epithelial cells of the alveoli. The microscope shows that 
the cells of the actively secreting gland are larger than those 
in the resting gland and more or less filled with fat globules, 
especially on the side toward the cavity of the alveolus. It was 
held that while this process went on the cell divided, forming 
two or more, and that finally the cell next to the cavity liquefied, 
setting free the fat globules which it contained and, perhaps 
with the addition of more or less water, constituted the milk. 
Milk production was thus regarded as a form of the growth of 
tissue. 



MILK PRODUCTION 465 

Subsequent investigation, however, has generally failed to 
show satisfactory evidence of cell division. A modification 
of Virchow's theory still held is that while there is no cell division, 
the outer portion of the protoplasm is sloughed off and dissolved, 
forming the milk, and is again renewed by the growth of new 
protoplasm. The weight of opinion, however, regards milk 
production as a true secretion, entirely analogous to that ob- 
served in other glands. It is not believed that there is normally 
a breaking down of cells, but that the latter extrude their 
secreted materials into the alveolus precisely as do the secreting 
cells of other glands. This is held to apply to the fat globules 
as well as to the other ingredients of milk. The process is in 
many ways analogous to that of the resorption of digested 
material by the epithelial cells of the small intestine, the obvious 
difference being the direction in which the materials move. 

The secretion of milk in the active udder is a more or less 
continuous process, the product accumulating in the cavities 
and passages of the gland. Fleischmann long ago showed, 
however, that the cavities of the udder cannot possibly contain 
the amount of milk produced in a single milking by a reason- 
ably productive cow, and it is well recognized that a rapid secre- 
tion of milk occurs during suckling or milking. In other words, 
the milk gland, like other glands, reacts to a specific stimulus. 

551. Sources of ingredients of milk. — While the ultimate 
source of the material contained in the milk is of course the 
feed, the milk gland draws its supply of material for milk pro- 
duction immediately from the blood, while at the same time it 
brings about extensive chemical transformations in the sub- 
stances thus supplied. Probably all the ingredients of the 
milk should be regarded as products of the chemical activity 
of the epithelial cells of the glands, although the extent to which 
the original material is modified varies. 

552. Origin of milk proteins. — The albumin and globulin 
of milk are quite similar to the corresponding substances in the 
blood. The casein, on the other hand, is radically different. 
In the first place, it is, as already stated, a conjugated protein 
containing some phosphorus-bearing radicle. Whether the 
latter is derived exclusively from the organic phosphorus com- 
pounds of the feed has not been demonstrated, although it 
appears probable that inorganic phosphorus compounds (phos- 

2 H 



4 66 



NUTRITION OF FARM ANIMALS 



phates) may be utilized as sources of the phosphorus of the milk 
(257, 258, 497). 

The production of casein, however, is not simply a conju- 
gation of a simple protein with a phosphorus group. The 
constitution of casein is markedly different from that of the 
proteins of the blood serum or of the muscles, as is shown by 
the proportions of its various cleavage products as given in 
Chapter I (50) , so that if casein is formed from the protein of the 
blood or tissue, a considerable reconstruction of their mole- 
cules is necessary. On the other hand, if the casein of the milk 
is built up in the epithelial cells of the udder, in the manner 
suggested in Chapter V (226, 227), from the simpler cleavage 
products in the blood, the process is specific for the milk gland. 

553. Origin of milk fats. — It was stated in Chapter V (247- 
249) in discussing the sources of body fat that although the latter 
may be derived in part from the fat of the feed and show some 
of its characteristics, nevertheless, the production of fat must 
be regarded as due essentially to the activity of the fat cells, 
and not to a simple deposition. 

In the first place, it has been demonstrated by the researches 
of Jordan and others that milk fat as well as body fat may be 
formed from the carbohydrates of the feed. 

In Jordan's l experiments cows were fed either with an ordinary 
ration or with one very poor in fat and the production of fat in the 
milk determined. After deducting the maximum amounts of fat 
which could possibly be accounted for by the protein and fat of the 
feed, a considerable balance was left which could only have been pro- 
duced from the carbohydrates. The following table gives a summary 
of the results : — 

Table 122. — Production of Fat by Cows 



Number 
of Days 


Total Pro- 
tein 2 Metab- 
olism 


Equivalent 
Fat 


Fat of 
Feed 


Total from 
Fat and 
Proteins 


Fat Actually 
Produced 


59 

74 
4 


Grams 

15,109 

34,661 

2,209 


Grams 

7,766 

17,816 

1,131 


Grams 
1,490 
2,211 
1,504 


Grams 

9,256 

20,027 

2,635 


Grams 
17,585 
37,637 

3,289 



1 N. Y. (Geneva) Expt. Sta., Buls. 132 and 197. 

2 Digested protein of feed less gain of protein by the animal. 



MILK PRODUCTION 467 

It should perhaps be pointed out that the formation of fat from 
carbohydrates in these experiments may not necessarily have occurred 
in the milk gland itself. It is entirely conceivable that the main 
portion of the synthesis of the fat may have taken place elsewhere 
and that the fat or its precursors were simply transferred to the milk 
gland. 

Second, it has also been shown by a considerable number of 
experiments that, as in the case of body fat, the fat of the feed 
may sensibly affect the properties of the milk fat. Not only 
have changes in the melting point, iodin number, and other 
properties of butter fat been found to follow in a general way 
similar changes in the feed fat, but characteristic ingredients 
of foreign fats given in the feed have been detected in the milk. 
While it is not necessary to conclude, and is indeed unlikely, 
that the feed fat is simply transferred, as it were mechanically, 
to the milk, it is clear, on the other hand, that relatively large 
fragments of the fat molecule are able to pass through the 
epithelial cells into the milk. These facts render it evident 
that feed fat is a source of milk fat. Not only so, but experi- 
ments by Morgen and his associates, to be mentioned later (613), 
seem to show that a certain amount of fat in the feed (in her- 
bivorous animals at least) conduces to the most efficient pro- 
duction of milk fat. 

The idea that the fat of milk is produced synthetically to a 
considerable extent is perhaps supported also by the presence 
in it of the lower acids of the aliphatic series, which may be 
intermediate steps in the synthesis of fat from simpler carbon 
compounds, or, on the other hand, may arise during the partial 
breaking up of the carbon chain in the feed fat which probably 
precedes its transformation into milk fat. 

As a general conclusion, therefore, it may be stated that the 
fat of milk may have its origin either in the fat or in the carbo- 
hydrates of the feed, or in both. Whether it may also be pro- 
duced from protein has not been demonstrated experimentally, 
but reasoning by analogy with the formation of body fat, it 
must be regarded as at least very probable. 

554. Origin of lactose. — The lactose of milk is a disaccharid 
yielding upon hydration dextrose and galactose. Dextrose or 
its derivatives are abundant in the feed of herbivorous animals 
and it is also a constant ingredient of the blood. On the other 



468 NUTRITION OF FARM ANIMALS 

hand, while the ordinary feed of herbivora contains carbohy- 
drates yielding galactose, the latter is apparently transformed 
into glycogen quite promptly and at any rate has not been 
found in the blood, while animals receiving feed containing no 
galactose (carnivora, e.g.) produce lactose in their milk. The 
probability seems to be that the galactose half of the lactose 
is manufactured in the milk gland from the dextrose of the 
blood. 

555. Sources of ash. — The ash ingredients of the milk, 
including its sulphur and phosphorus, are, of course, derived 
ultimately from the corresponding ingredients of the feed. In 
liberal milk production on ordinary winter rations containing 
a sufficiency of organic nutrients, however, it appears from in- 
vestigations by Forbes 1 that considerable amounts of calcium, 
magnesium and phosphorus may be drawn from the relatively 
large store contained in the body, presumably to be replaced 
in later stages of lactation. 

556. Character of milk production. — While the statement 
that milk production is a form of tissue growth is probably 
incorrect anatomically, it is essentially true so far as the chemical 
composition of the product and the demands which it makes 
on the feed supply are concerned. This is clearly shown by 
comparing the ratio of protein to fat in the organic matter of 
milk and in that of the increase in weight of growing animals. 
In the solids of milk, it is evident that in order to make a fair 
comparison its milk sugar should be reduced to the equivalent 
amount of fat. Taking Babcock's figures (547) as representing 
the average composition of milk, the 4.88 per cent of sugar di- 
vided by 2.25 is equivalent to 2.17 per cent of fat, which added 
to the 3.69 per cent of fat present as such makes a total fat 
equivalent of 5.86 per cent, while if milk sugar were thus re- 
placed by fat the total organic matter would amount to 9.41 
per cent. On this basis, 100 parts of organic matter would 
contain 37.73 per cent of protein and 62.27 per cent of fat. 
Comparing these figures with those given in Chapter XI (458) 
for the composition of the increase in growth, it appears that 
the proportion of protein to fat is greater than that computed 
for young animals except in the earliest stages of growth. 

The computed energy content of average milk solids is 2620 

1 Ohio Expt. Sta., Bui. 295 (1916). 



MILK PRODUCTION 469 

Cals. per pound. This is greater than the energy content of 
the dry matter gained by very young animals, but less than 
that computed in later stages of growth. In a general way, 
then, it may be said that milk solids correspond in proportion 
of protein and in energy value per pound to the gains made by 
growing animals when in the neighborhood of three months old. 

557. Rate of production of milk solids. — A beef calf three 
months old may be assumed to make a growth of approximately 
1.5 pounds per day, containing perhaps three-fourths of a pound 
of dry matter with an energy content of about 2200 Cals. 
The very moderate yield of 15 pounds of average milk per 
day would contain about 1.92 pounds of total solids equiva- 
lent to 5030 Cals. of energy. In other words, considerably 
more than twice as great a production would be effected by the 
relatively small bulk of the secreting cells in the udder as by 
the whole body of the calf. When it is further considered 
that the product of the dairy cow is all edible, her great 
economic value as a producer of human food becomes ob- 
vious. On this point Jordan says : 1 " A cow yielding 6000 
pounds of average milk per year is not regarded as an 
unusual animal. This means, however, the annual produc- 
tion of not less than 780 pounds of milk-solids, an amount 
at least double the dry matter in the body of a cow weighing 
900 pounds. When we consider that this manufacture of new 
material is carried on not only during a single year, but through 
the entire adult life of the animal, we begin to realize how ex- 
tensive are the demands upon the food supply. Still more 
striking is the case of high-grade cows yielding annually over 
half a ton of milk solids, and when we remember the perform- 
ance of Clothilde, whose 26,000 pounds of milk produced in 
a year certainly contained more than 2500 pounds of solid 
matter, we must regard the cow as possessing wonderful powers 
of transmutation. Her capacity for the rapid and economical 
production of human food of the highest quality is not equaled 
by any other animal." 

558. Factors of milk production. — Milk production differs 
from meat production in one very essential particular. In the 
latter, broadly speaking, an increase in the whole body of the 
animal is what is sought, and while the product may vary in 

1 The Feeding of Animals, 1908, p. 308. 



470 NUTRITION OF FARM ANIMALS 

market quality, all the feed consumed in excess of the main- 
tenance requirement is available for the production of gain. 
In milk production, on the contrary, what is desired is the 
secretion of a single set of glands. An increase in weight in 
the mature dairy cow is not sought. At best it represents a 
diversion of feed to other purposes than the one in view, while 
any considerable fattening tends to check the activity of the 
milk glands. In feeding for milk production, therefore, it is 
necessary to consider not only the surplus feed above the main- 
tenance requirement but the factors affecting the distribution 
of that surplus between milk production on the one hand and 
growth or fattening on the other hand. The art of feeding for 
milk consists in stimulating the milk production to the greatest 
economically possible extent and in supplying .the feed material 
necessary for this production, while avoiding, in the mature 
animal, any material increase of body tissue. 

The factors governing milk production are essentially the 
same as in other branches of animal production, viz., the ani- 
mal, the environment and the feed supply. 

In milk production, however, the relative importance of the 
first and second conditions is greater than in other forms of 
production for the reason that they may materially influence 
the distribution of the excess feed between milk production and 
tissue increase. 

§ 2. The Animal as a Factor in Milk Production 

559. The prime factor in successful dairy production is the 
animal. Unless the latter possesses abundant secreting tissue 
which is capable of being stimulated to a normal rate of activity 
and of yielding a secretion of good quality, the most scrupulous 
care and the most abundant feeding will inevitably fail to yield 
satisfactory returns. 

Individuality 

560. Includes breed differences. — The influence of in- 
dividuality may be said to include that of breed, since a breed 
is simply an aggregate of more or less similar and genetically 
related individuals. It is outside the scope of this work to 
discuss problems of breeds and breeding, and this branch of the 



MILK PRODUCTION 



471 



subject will therefore be considered mainly from the point of 
view of individual differences. 

561. Influence on yield of milk. — While the actual quantity 
of milk produced is affected by feed, care and other circum- 
stances, the capacity of the animal as a milk producer is an 
individual characteristic. Just as the maximum speed of 
which a horse is capable is dependent primarily upon his con- 
formation, spirit and other individual characteristics, while 
the actual rate at which he travels at any given time is largely 
dependent upon his driver, so the maximum capacity of the 
milk cow constitutes an individual limit beyond which she can- 
not be pushed by any amount of care or feed. 

Striking illustrations of the importance of individuality are afforded 
by the various public tests of dairy cows. For example, in the 
World's Columbian Exposition of 1893, the conditions of the so-called 
ninety-days test were such as to induce liberal feeding and the best 
of care on the part of the exhibitors. The cows, numbering 74, were 
of three different breeds and presumably represented the best avail- 
able specimens of each breed. 

The following table shows the average daily product of the best l 
and the poorest cow of each breed in that test. 

Table 123. — Average Daily Yield of Cows in Ninety-Days Test, 
World's Columbian Exposition 2 



Best Jersey 

Poorest Jersey 

Poorest in per cent of best 

Best Guernsey 

Poorest Guernsey . . . . 
Poorest in per cent of best 

Best Shorthorn 

Poorest Shorthorn .... 
Poorest in per cent of best 



Milk 



Fat of Milk 



40.4 lb. 
22.9 lb. 
56.7% 

39.0 lb. 
19.3 lb. 

49-5 % 

40.9 lb. 
23.9 lb. 

58.4% 



Total Solids 
of Milk 



1.98 lb. 
1.09 lb. 

5S-i% 

1.70 lb. 
0.97 lb. 

57-i% 

1.49 lb. 
0.80 lb. 
53-7% 



5-67 lb. 
3.21 lb. 

56.6% 

5-39 lb. 
2.75 lb. 

5i.o% 

5.29 lb. 
2.87 lb. 
54.3% 



1 By best and poorest cows is meant those which showed the greatest and least 
net profit under the rules of the test. 

2 Jersey Bulletin, Dec. 12, 1893. 



472 NUTRITION OF FARM ANIMALS 

Even the lowest of these records are remarkably good considering 
the unfavorable conditions necessarily incident to a public test. In 
each of these three picked herds, however, the production of the 
poorest animal was only from 50 to*6o per cent of that of the best 
animal. Moreover, the differences between individuals of the same 
breed were much greater than the differences between the averages 
for the three breeds. That even greater differences exist among the 
common cows of the country has been shown by numerous statistical 
investigations, some of the most striking of which have been col- 
lected by Eckles. 1 

562. Influence on economy of feeding. — While it is un- 
likely that the utilization of the feed in the narrower sense 
(i.e., the amount of milk solids of a given composition manu- 
factured in the udder from equal amounts of nutritive substances 
supplied) is materially affected by the individuality of the 
animal, the feed utilization in the broader economic sense is 
very largely dependent upon this factor. It must be con- 
stantly borne in mind that, as already stated (558), efficiency 
in milk production is in large part a question of the distribution 
of the feed supplied in excess of maintenance. Some animals, 
by virtue of individual or inherited peculiarities, are able to 
transform large amounts of excess feed into milk without stor- 
ing up any considerable portion of it in the form of body tissue. 
Such animals tend to remain spare in body and if well fed 
produce large amounts of milk. They are the typical dairy 
animals. Other individuals, on the contrary, have a well- 
marked tendency in the opposite direction, viz., toward the 
production of body tissue. When fed heavily, they utilize 
the additional feed chiefly in this direction and show little or 
no tendency toward an increase in milk production. These 
are typical meat-producing animals. The two types, of course, 
shade into each other by imperceptible gradations. 

The important bearing of these facts upon the nutrition of 
dairy animals will be further considered later (606-610). 
Here it may simply be noted that the superiority of cer- 
tain individuals which has been illustrated in the preceding 
paragraphs is doubtless due to a considerable extent to the 
ability to consume large amounts of feed and convert the sur- 
plus into milk rather than into body tissue. 

1 Dairy Cattle and Milk Production, 191 1, pp. 1 18-126. 



MILK PRODUCTION 



473 



563. Influence on course of lactation. — That individuality 
plays an important part in determining the rate at which the 
milk yield falls off with advancing lactation is shown more 
specifically in a subsequent paragraph (568). 

564. Influence on composition of milk. — It is a matter of 
common observation that cows vary as regards the richness 
of their milk, that is, as regards the amount of cream or butter 
which can be obtained from a given weight of milk. Various 
breed tests at experiment stations have served to define more 
exactly the influence of individuality and breed upon the com- 
position of milk. The results cited in Table 1 24 are intended 
to illustrate this influence and not primarily to compare dif- 
ferent breeds. The table shows the averages of the results ob- 
tained at three different experiment stations 1 for several breeds 
in tests covering periods of time ranging from eight months to 
two years. The results from each station are given weight 
in the average in proportion to the number of cows under 
test, and the average results are arranged in the order of the 
fat content of the milk. 

Table 124. — Average Composition of Milk of Different Breeds 



Ash 



Casein 
and 

Albu- 
min 



Lac- 
tose 



Fat 



Total 
Solids 



Num- 
ber OF 
Cows 
Aver- 
aged 



Holderness . . 
Holstein-Friesian 

Ayrshire . . 

Shorthorn . . 

Devon . . . 

Guernsey . . 

Jersey . . . 



% 
0.68 
0.67 
0.67 

o.73 
0.76 

0.75 
o.75 



% 

3-14 
3.22 

IS* 
3-27 
3-74 
3.78 
3-92 



% 

5-n 
4.89 

S-i3 

4.80 

5-3 2 
4.94 
4.98 



% 
346 
3-5i 
3-64 
3-65 
4-54 
4.96 

5-25 



% 
12.39 
12.29 
12.82 
12.45 
14.36 

1443 
14.90 



% 
2 
6 
9 
3 
2 

5 



Fat is evidently the most variable ingredient of milk, its 
maximum exceeding its minimum in these averages by more 
than 50 per cent. Along with the increase of fat there is 



1 Maine Expt. Sta., Rpt. 1890, p. 29; New Jersey Expt. Sta., Rpt. 1890, pp. 223- 
224; New York (Geneva) Expt. Sta., Rpt. 1891, pp. 94-104. 



474 



NUTRITION OF FARM ANIMALS 



also an increase of the total protein and of the total solids, 
but these are relatively smaller than that of the fat, the totals 
being 25 per cent and 21 per cent, respectively. There is also 
an increase of 12 per cent in the proportion of ash, while the 
lactose, on the contrary, shows comparatively small and ir- 
regular changes, the extreme range of the differences being 
11 per cent, while it does not increase regularly with the in- 
crease of the other ingredients. The lactose is evidently the 
most constant ingredient of the milk. 

565. Influence on composition of milk solids. — The real 
nature of the differences in composition, however, is rendered 
clearer by computing the percentage composition of the water- 
free total solids, with the results shown in Table 125 : — 

Table 125. — Average Composition of Milk Solids of Different 

Breeds 



Holderness . . 
Holstein-Friesian 

Ayrshire . . . 

Shorthorn . . . 

Devon . . . 

Guernsey . . , 

Jersey . . . , 



Ash 



% 



5-49 
5-45 
5-23 
5-86 

5-29 
5.20 

5-o3 



Casein 

• AND 

Albumin 



% 

25-44 
26.20 
26.37 
26.27 
26.04 
26.20 
26.31 



Lactose 



% 

41.24 

39-79 
40.01 

38.55 
37.06 

34-23 
33-42 



Fat 



% 

2 7-93 
28.56 
28.39 
29.32 
31.61 
34-37 
35-24 



Num- 
ber OF 
Cows 
Aver- 
aged 



% 
2 
6 
9 

3 

2 

5 



From the foregoing table, it appears that the percentages of 
ash and of total protein in the milk solids are very constant, 
the single figures differing but very slightly from the averages 
of 5.36 and 26.10, respectively. The essential difference in 
the composition of the milk solids lies in the proportion of 
lactose to fat, the former decreasing as the latter increases, 
while the total percentage of the two taken together is prac- 
tically constant, varying less than 0.7 per cent from the average 
of 68.53 per cent. In other words, it appears from these figures 
that in cows producing milk rich in fat the secreting cells form 
relatively less lactose and correspondingly more fat, while, as 



MILK PRODUCTION 



475 



Table 124 shows, this difference is accompanied by a rela- 
tively smaller secretion of water, so that the percentage of total 
solids in the resulting milk is greater. 

Cooke, 1 in 1890, drew the same conclusion from a study of 
over 2400 analyses of milk reported by the experiment sta- 
tions of the United States up to that date, and more recently 
Haecker 2 has reached substantially the same result from 
analyses of 544 individual samples of milk from the Minnesota 
Station herd. 

566. Variability of composition in same animal. — It should 
be noted that the foregoing conclusions are drawn from 
the average composition of the milk of the same individuals 
for comparatively long periods. The composition of the milk 
of the same cow, however, may and frequently does vary quite 
widely from one milking to another without affecting its average 
composition as computed from analyses of a number of milkings. 
This has been observed especially in the case of the fat be- 
cause far more determinations have been made of this con- 
stituent than of any other, the fat being both the most valuable 
and the most easily determinable ingredient. Variations as 
great as 1 per cent in the fat content of successive milkings of 
the same cow are not uncommon and differences of 2 and even 
3 per cent not very rare. Whether there is a correlated varia- 
tion in the proportion of lactose, as in the averages compared 
in the previous paragraph, does not appear. It is presumed 
that these variations are due largely to external influences but 
no definite connection with any specific factors of environment 
has been traced with certainty, although Spier 3 believes them 
to be due to incomplete milking (575) . It is evident that correct 
comparisons of the yields of different animals, or of the same 
animal at different times, can be made only on the basis of the 
average yield and composition for a number of days. 

The extent of this variability in the composition of milk from 
one milking to another appears to be an individual peculiarity, 
the milk of some cows being much more uniform in daily com- 
position than that of others. An interesting example of this 
has been reported by Farrington. 4 

1 Vt. Expt. Sta., Rpt. 1890, pp. 97-100. 

2 Minn. Expt. Sta., Bui. 140 (1914), p. 51. 

3 Jour. Highland and Agr. Soc, 1909, p. 287. 

4 Ills. Expt. Sta., Bui. 17 (1891), p. 9. 



476 NUTRITION OF FARM ANIMALS 

Stage of lactation 

567. Milk production a periodic function. — Milk produc- 
tion has as its object the nourishment of the offspring. In a 
state of nature it is a periodic function, beginning at the birth 
of the young or shortly before, while as the young animal gradu- 
ally becomes less dependent on the mother it diminishes in 
intensity and finally ceases. Although man has greatly pro- 
longed the period of milk production of the cow, so that the 
time during which she goes dry is relatively short and in some 
instances is eliminated altogether, nevertheless, milk production 
still retains its periodic character and undergoes marked changes 
during the progress of a lactation. 

568. Influence on yield of milk. — The most evident effect 
of advancing lactation is the gradual decrease of the amount 
of milk produced, but the rate of decrease may differ widely 
at different stages in the same animal and in different animals 
at the corresponding period in lactation. As a rule, the amount 
of milk does not reach its maximum immediately after the birth 
of the young, but shows an increase for one or two weeks in 
the case of the cow. Following this maximum, there is typi- 
cally a slow falling off for several months followed by a more 
rapid decrease as the time of the next calving approaches, all but 
exceptional cows going dry for a longer or shorter time. In the 
case of farrow cows, the milk production may continue to show 
a comparatively slow decrease for a much longer time. 

The curves of lactation as they may be called, however, vary 
greatly from cow to cow and from year to year with the same 
animal and show marked irregularities often not readily ex- 
plained by any observed conditions. 

569. Influence on composition of milk. — In general the 
percentages of total solids and of fat tend to increase, especially 
toward the end of lactation when the quantity of milk falls off 
rapidly. Like the changes in quantity, these variations in 
composition are often irregular and sometimes are scarcely 
manifest at all until the rapid falling off in quantity sets in 
toward the end of the lactation. 

570. Bearing on experimental methods. — The unavoidable 
changes in the yield and composition of milk with the advance 
of lactation must be taken account of in all experiments on 



MILK PRODUCTION 477 

milk production, and render the interpretation of their results 
peculiarly difficult. It is obvious, e.g., that if a change of the 
ration of a cow is accompanied by a decrease in her milk yield 
part at least of the decrease may be due to the progress of lac- 
tation and not to the change of feed. On the other hand an 
increase of the milk yield in a later period of the experiment 
may be partly offset by the natural shrinkage in milk. In 
brief the later periods of an experiment are at a disadvantage 
compared with the earlier periods. 

Two methods for eliminating or attempting to eliminate this 
influence of lactation have been used, viz., the period system 
and the group system. 

571. The period system. — In the period system, as intro- 
duced by Wolff, Kiihn and others of the earlier experimenters, 
the animal receives an identical ration in two or more periods 
well removed from each other in point of time — usually the 
first and last periods — and from the results of these periods the 
average daily rate of decrease in the yield of milk and its in- 
gredients is calculated. On the assumption that had the same 
ration or treatment been continued unchanged this rate would 
have been uniform throughout the experiment, it may be 
computed what yields would have been secured in the inter- 
mediate periods. A comparison of these computed yields with 
those actually observed is taken as the measure of the effect 
of the change in feed or other conditions. The accuracy of 
this method depends of course on the correctness of the as- 
sumption that the yields would have decreased at a uniform 
rate. 

572. The group system. — The use of the group system was 
introduced by Fjord and his successors in the Copenhagen 
Experiment Station in connection with their determinations of 
the so-called feed units (702). The period system seeks to 
compare each animal with itself. The group system, on the 
other hand, attempts to compare an animal or group with an- 
other check animal or group. In a long preliminary period 
both groups receive the same ration or treatment and their 
relative production is determined. One of the groups is then 
continued on the same treatment while with the other group 
the factor to be tested is introduced. Finally, in a concluding 
period, both groups are again treated as in the initial period. ' 



478 NUTRITION OF FARM ANIMALS 

A combination of the two systems may also be used, one 
group of animals being fed varying rations in successive periods, 
while the other receives a uniform ration throughout the entire 
experiment. 

A very complete discussion of the methods of eliminating the in- 
fluence of advancing lactation in the interpretation of the results of 
experiments on milk production is to be found in a recent article by 
Morgen. 1 

§ 3. The Influence oe Environment on Milk Produc- 
tion 

The word environment is here used loosely as a convenient 
term to summarize all those external influences other than feed 
which may affect milk production. The dairy cow appears 
to be particularly sensitive to external conditions, some of the 
more important of which are considered in the following para- 
graphs. 

Milking 

Milking is but an imperfect imitation of the suckling of the 
young, and naturally its efficiency in securing the milk is likely 
to be affected by a variety of circumstances. 

573. Frequency of milking. — As already stated, the cavities 
of the udder in heavy milkers cannot hold all the milk produced 
at one milking. Between milkings there evidently may be a 
considerable accumulation of matter in the alveoli and canals 
which appears to have the effect of diminishing the secreting 
activity of the epithelial cells through what might be crudely 
called " back pressure." Suckling or milking would have the 
effect of relieving this " pressure " and perhaps rendering 
secretion more easy, while at the same time it seems to act as a 
direct stimulus to secretion. At any rate it is a fact that more 
frequent milking tends to increase the yield of milk, especially 
in the case of good cows and in the earlier stages of lactation. 
The effect of frequent milking is strikingly illustrated in the 
following experiments by Kaull. 2 The abrupt falling off in the 
milk yield when the milking was made very frequent may per- 

■ * Landw. Vers. Stat., 77 (191 2), 351. 
2 Cited by Kellner, Die Ernahrung der landw. Nutztiere, 6th Ed., p. 521. 



MILK PRODUCTION 



479 



haps be interpreted as due to overstimulation or mechanical 
irritation of the udder. 

Table 126. — Effect of Frequent Milking 





Total Quantity 


Total Quantity 




of Milk per 


of Milk in 24 




Milking 


Hours 


Milking every 24 hr 


3.8i Kg. 


7.62 Kg. 


Milking every 2 hr 


2.46 Kg. 


9.84 Kg. 


Milking every 4 hr 


2.06 Kg. 


12.36 Kg. 


Milking every 2 hr 


1. 11 Kg. 


13.32 Kg. 


Milking every 65 min 


0.66 Kg. 


14.62 Kg. 


Milking every 50 min 


0.07 Kg. 


2.02 Kg. 



Results obtained in short experiments, however, give an 
altogether exaggerated idea of the practical advantage of fre- 
quent milking. As Fleischmann has shown, the capacity of 
the udder adjusts itself quite definitely to its productive activity 
and in the measure in which this takes place the gain due to 
more frequent milking diminishes or disappears. He estimates 
the increased yield obtained by three as compared with two daily 
milkings at about 6 or 7 per cent. In many cases, therefore, 
it will be questionable whether the additional milk obtained by 
a third milking will be at all sufficient to pay for the extra labor 
involved. In the case of very productive cows in the earlier 
stages of lactation more frequent milking may be necessary, 
not so much for the sake of obtaining the extra milk as for the 
sake of avoiding inflammatory conditions in the udder and es- 
pecially for preventing the permanent depression of the secret- 
ing power which would follow incomplete milking and which 
would mean a loss of milk throughout the whole lactation. 

574. Influence of frequent milking on composition of milk. — 
Frequent milking tends to increase the percentage of solids and 
of fat in the milk. This effect is manifest especially when the 
intervals between the milkings are of unequal length. 

When milking takes place at regular intervals, the several 
milkings tend to have about the same average composition. 
If the intervals vary in length, the milk obtained after the 
shorter interval on the average contains a higher percentage of 



480 NUTRITION OF FARM ANIMALS 

solids and of fat, i.e., it is more concentrated than that yielded 
after the longer interval. The differences in the composition 
of the night's and morning's milk, which have been the subject 
of so much discussion, appear explicable upon this basis, the 
interval between the morning's and night's milking being usually 
less than that between the night's and morning's. 

575. Completeness of milking. — If successive portions of 
the same milking be analyzed, the percentage of fat in the later 
portions will be found to be greater than in the earlier ones, 
while the percentage of solids-not-fat varies comparatively 
little. The fact of the greater richness of the so-called " strip- 
pings " is well known. This difference was at one time ex- 
plained as caused by an actual rising of the cream on the milk 
contained in the udder. The fact, however, that but a com- 
paratively small amount of milk is held in the milk cistern, as 
well as the entire anatomy of the udder, renders this explanation 
untenable. The difference is probably due to a partial retention 
or stagnation of the fat globules in the alveoli and canals, they 
being afterward washed out by the portions of milk secreted 
during the latter part of the milking. Incomplete milking 
not only fails to get this fat, thus lowering the quality of the 
milk actually obtained (compare 566), but it appears that 
the retention of the fat in the alveoli tends to check the 
secretion of the milk. In all forms of milking, therefore, it 
is important that the cow be milked out as completely as 
practicable. The advantages of various methods of manipulat- 
ing the udder, such as the Hegelund method, are probably due 
largely to this influence. Similarly, in the use of milking ma- 
chines it seems to be necessary with most cows to remove 
the last portions, or strippings, by hand. 

Muscular exertion — exercise, fatigue 

The influence of muscular exertion upon milk secretion has 
been much discussed upon a comparatively slender experi- 
mental basis. In the United States the question has usually 
been as to the desirability of allowing freedom of motion and 
exercise to dairy cows, while in Europe, especially among 
small farmers, cows are used for draft to a not inconsiderable 
extent. 



MILK PRODUCTION 481 

576. Feed cost of exercise. — Attention was called in the 
discussion of the maintenance requirement in Chapter VIII 
(391) to the very marked effect of muscular exertion in increas- 
ing the katabolism, especially of body fat or of the non-nitroge- 
nous ingredients supplied by the feed. It has been frequently ar- 
gued from this fact that the amount of exercise allowed to dairy 
cows should be restricted as much as possible. Not a few dairy- 
men indeed have gone so far as to confine their cows entirely, 
reasoning that since the object of their business is to convert 
feed into milk any diversion of it to the support of muscular 
exertion was a waste. This, however, is a very narrow and 
inadequate view of the subject. Most authorities on dairying 
regard a moderate amount of exercise for dairy cows as bene- 
ficial. Thus Martiny * in 1871 cites five authorities on this 
point and expresses the opinion that exercise and moderate 
work increase rather than decrease the yield of milk, while 
severe work has an unfavorable effect upon both the yield and 
quality. Similar opinions are expressed later by C. F. Miiller, 
Fleischmann, Kirchner, Konig and Von Klenze. These earlier 
data are of the nature of more or less empirical observations 
rather than of actual experiments. 

577. Morgen's investigations. — Of actual experiments upon 
the influence of muscular exertion upon milk production, 
those of Morgen 2 at the Hohenheim Experiment Station are 
the most convincing because they were made under strictly 
comparable conditions and especially because the relative 
amounts of work performed in the different periods were 
determined. 

The two Simmenthal cows employed were accustomed to 
being used for draft. The work was done at a slow walk upon 
the sweep power dynamometer used by Wolff in his experiments 
upon work production by the horse (386 a, 670, 779), the amount 
of work performed being regulated in part by the resistance of 
the dynamometer and in part by the number of hours of work 
required, so that approximately single, double and quadruple 
work was done. The ration fed, which was a liberal one, was 
unchanged throughout the trials. The experiment consisted 
of 1 1 periods, approximating two weeks 3 each of alternate rest 

1 Die Milch, Part I, pp. 345-435- 2 Landw. Vers. Stat., 51 (1899), 117. 

3 Eleven to twenty-six days. 

2 I 



482 NUTRITION OF FARM ANIMALS 

and work periods, beginning with a rest period, so that each 
work period was preceded and followed by a rest period. 

The rather moderate amount of work performed caused some 
decrease in the volume of milk produced, the effect tending to 
be a little greater in the periods in which most work was done. 
The decrease, however, was chiefly a decrease in the amount 
of water secreted, although a slight diminution in the yield of 
total milk solids, ranging from 10 to 85 grams per day, was ob- 
served. In other words, the effect of the work was to render 
the milk somewhat more concentrated. The most notable 
effect, however, was upon the yield of fat, which showed an 
actual increase in every case but two. This increase was com- 
pensated for by a decrease of the fat-free solids, so that analyses 
of the milk showed a higher percentage of fat and of total solids, 
while the percentage of fat-free solids remained practically un- 
changed. 

578. Confirmatory results. — Quite similar results, although 
obtained in some cases by less rigorous methods, have been 
reported by Dornic, 1 Stillich, 2 Backhaus, 3 Torssell 4 and Dol- 
gich. 5 

Observations by Sturtevant, 6 Henkel 7 and Hills 8 upon the 
effect of fatigue on the yield and composition of milk are also 
in accord with the results of experiments upon work and ex- 
ercise in showing a tendency to reduce the quantity of milk 
and at the same time to increase both the percentage and the 
actual yield of fat. 

Aside from the question of the effects of overexertion, it 
appears clear that a considerable amount of work may be per- 
formed by cows without any serious diminution of the volume 
of their milk and with an actual increase in the yield of fat, its 
most valuable ingredient. The lightest work in Morgen's 
experiments was roughly equivalent to hauling a load of a ton 
if miles over a smooth level road. This is certainly much more 
labor than the ordinary cow will perform when turned loose in 
a comfortable yard or paddock. 

1 Milch Ztg., 25 (1896), 331. 2 Jahresber. Agr. Chem., 39 (1897), 529. 

3 Centbl. Agr. Chem., 28 (1899), 492; Expt. Sta. Rec, 10 (1899), 85. 

4 Expt. Sta. Rec, 12 (1901), 381. 5 Jahresber. Tier Chem., 33 (1904), 382. 
6 N. Y. (Geneva) Expt. Sta., Rpt. 1882, p. 25. 

7 Landw. Vers. Stat., 46 (1896), 329. 

8 Vt. Expt. Sta., Rpts. 1894, p. 162, 1898, p. 367 and 1899, p. 309. 



MILK PRODUCTION 483 

It is still true, of course, that the energy for all muscular 
exertion is ultimately supplied by the feed. In the instance 
just mentioned the extra feed required for this purpose may 
be approximately estimated, on the basis of the data contained in 
Chapter XIV, at two-thirds of a pound of digestible matter per 
day, equal to about eight-tenths of a pound of maize. The feed 
cost of the exercise ordinarily taken by cows turned out in the 
yard must be insignificant and be far outweighed by the tonic 
effects of fresh air, sunshine and freedom on their health and 
general condition, while in the case of heavily fed cows some 
exercise may possibly be of advantage in diminishing the tend- 
ency to fatten. The question of turning out dairy cows for 
exercise, then, virtually reduces itself to the question whether 
the cost of the labor involved is repaid by the effect upon 
the health of the animals. 

Temperature. Shelter 

579. Air temperature. — The general principles regarding 
the relations between external temperature, heat production 
and feed supply, already discussed in Chapters VII (350-356), 
VIII (395-397) and XII (535-543), apply also to the dairy cow. 
Like the beef steer, the well-fed dairy cow in full flow of milk is 
consuming a large excess of feed above her maintenance ration 
and is producing a correspondingly large amount of heat. 

For example, in an experiment reported by Jordan 1 the computed 
heat production of two cows (disregarding slight changes in weight) 
and the estimated amount of heat which would have been produced 
on a maintenance ration were as follows : — 

Table 127. — Estimated Heat Production of Cows 

Cow No. 10 Cow No. 12 

Weight 775 Lb. 1200 Lb. 

Computed heat production . . 18.67 Therms 21.10 Therms 
Estimated heat production on 

maintenance ration . . . . 10.10 Therms 1 3-7o Therms 

The heat production was greater in one case by 85 per cent and 
in the other by 54 per cent than the estimated amount on maintenance, 
which is a considerably greater excess than that computed (537) for 
Kellner's fattening steers. 

1 The Feeding of Animals, The Macmillan Co., New York, 1908, p. 310. 



484 NUTRITION OF FARM ANIMALS 

So far as mere maintenance of body temperature goes, then, 
no reason appears why a cow might not be subjected to com- 
paratively low temperatures without causing any increased 
katabolism for the sake of heat production solely. That the 
same factors of size and weight, humidity of air, and the amount 
and character of ration as in the case of the steer enter into the 
question is obvious. 

580. Shelter, etc. — The question of shelter does not differ 
in principle with the cow and with the steer. The influence of 
precipitation, wind, insolation and temperature of drinking 
water are the same qualitatively on the cow as on the steer and 
the same reasons which render shelter desirable in the one caze 
apply in the other. 

581. Modifying factors. — The foregoing facts, however, are 
scarcely sufficient to justify the conclusion that a dairy cow 
may be treated in this respect like a beef steer. In making a 
quantitative application of these facts in practice, certain 
modifying factors require consideration. 

Relative body surface. — Even the most casual comparison 
of the dairy cow with the beef steer is sufficient to show that 
they differ materially in form and to raise the supposition that 
the ratio of body surface to weight may vary considerably in 
the two types. The writer is not aware of any measurements 
of body surface of cows but one can hardly avoid the impression 
that the spare angular form of the typical dairy cow exposes 
relatively more surface than the compact, rounded form of the 
beef animal. 

Condition. — Outdoor winter feeding of cattle is practiced 
largely with fattening animals and it is with them that most 
experiments have been conducted. With such an animal a 
considerable covering of fat is usually acquired before the onset 
of extreme cold weather, while the typical dairy cow devotes her 
feed to milk production and carries very little body fat. There 
are no definite data as to the protective value of a fat covering 
but doubtless it is a poor conductor of heat and it would seem 
that it might have considerable influence in reducing radiation. 

Skin and hair. — The skin of the dairy cow is reputed to be 
thinner than that of the steer and may therefore be a better 
radiator of heat. The coat of hair of the cow, too, is apt to be 
shorter and lighter than that of the steer, whether as a result 



MILK PRODUCTION 485 

of breeding or of continuous shelter and warm quarters, and is 
to that extent a poorer protection against loss of heat. 

For all these reasons, it is clear that the loss of heat from the 
dairy cow may well be more rapid than that from the steer of 
like weight under the same external conditions and that con- 
sequently the minimum limit of external temperature below 
which additional katabolism is caused may be higher for the 
former than for the latter. 

582. The direction of production. — Another important 
consideration in connection with the question of temperature 
and shelter for dairy cows is that of their possible influence 
upon the direction of production. Stress was laid at the outset 
of this discussion of the factors of milk production (558) upon 
the essential difference between beef production and milk pro- 
duction due to the fact that in the latter it is simply the secre- 
tion of a single gland and not a general increase of the whole 
body which is desired. The activity of the milk gland, how- 
ever, is much more sensitive to external influences than, for 
example, that of adipose tissue. It is quite conceivable, there- 
fore, that a degree of cold or exposure which, from the standpoint 
of heat production merely, might not require any additional 
katabolism to maintain the body temperature, might neverthe- 
less check the formation of milk, especially if the cow were sub- 
jected to it suddenly. In such a case it would be anticipated, 
either that feed previously used for milk production would be 
stored up as body fat or else, if the cow continued to eat the 
same amount, would lead to a stimulation of the general body 
katabolism and so to an unnecessary increase in heat production. 

In other words, exposure to cold might conceivably neither 
increase the feed consumption nor diminish the total utilization 
of surplus feed but might, nevertheless, be a disadvantage be- 
cause it diverted the current of productive activities from the 
formation of milk to other and undesired forms of production. 

583. Results in practice. — Only meager experimental evi- 
dence is available regarding the practicable or desirable limits 
of temperature for dairy cows. 

Plumb l compared the feed consumption and milk yield of two 
lots of purchased cows, one of which was turned out into the yard 
about one hour per day on sunny days while the other was turned 
1 Ind. Expt. Sta., Bui. 47 (1893), pp. 89-96. 



486 



NUTRITION OF FARM ANIMALS 



out for eight hours every day without regard to the weather but with 
some shelter from the wind. The cows consumed feed ad libitum. 
The exposed lot ate much more grain but somewhat less hay than 
the sheltered lot and produced 161.1 pounds more milk. No proof of 
the comparability of the two lots is given. 

Brooks l exchanged two lots of cows between an artificially heated 
stable kept at 55 F. and a cooler, unheated one, the temperature of 
which is not reported. Rather more milk was produced in the warm 
stable but its percentage of fat was lower. 

Richards and Jordan 2 recorded the milk yield of a number of cows 
upon uniform feed in alternate periods in which the stable tempera- 
ture was maintained, respectively, at about 45 and 55 F. More 
milk was produced in three cases out of four and more butter fat in 
two cases out of four at the higher temperature. 

Spier 3 reports experiments at four farms, on a total of 88 animals 
upon the relation of stable temperature and ventilation to milk yield. 
He calls attention to the fact that both these factors are involved in 
experiments upon the influence of shelter. The following table shows 
the results obtained in two specially cold periods as compared with 
the average of warmer preceding and following periods and likewise 
the average results for the entire experiments. The average rations 
consumed are stated but there is no record of actual feed consumed 
during the several periods nor of the live weights of the animals. 

Table 128. — Influence of Ventilation and Stable Temperature 

on Milk Production 





Free Ventila- 


:ion 


Restricted Ventilation 




Milk per 


Fat in 
Milk 


Stable 


Milk per 


Fat in 
Milk 


Stable 




Day and 


Temper- 


Day and 


Temper- 




Head 




ature 


Head 




ature 




Lb. 


% 


°F. 


Lb.' 


% 


°F. 


Dec. 20-Jan. 4 














Warm periods . . 


29.0 


3-55 


53-76 


28.9 


3-48 


61.73 


Cold period . . . 


29.O 


3.5i 


41.20 


29.0 


3-53 


52-30 


Feb. 14-Mar. 27 














Warm periods . . 


25-3 


3-63 


50.3I 


25-4 


3-48 


60.11 


Cold period . . . 


254 


3-69 


46.07 


25-5 


3-5i 


56.67 


Entire Experiments 














Nov. 22-Mar. 27 . 


27-5 


3-55 


49.82 


27-3 


3-49 


59-40 



1 Mass. (Hatch) Expt. Sta., Rpt. 1895, p. 39. 

2 Wis. Expt. Sta., 21st Rpt., 1903-1904, p. 143. 

3 Jour, of Highland and Agr. Soc, 1909, pp. 255-306. 



MILK PRODUCTION 



487 



The foregoing results show no perceptible effects from the tem- 
perature fluctuations within the range of these experiments either on 
the lots kept in the cooler stables from the start nor on those in 
warmer quarters when the temperature of the latter fell. 

Davis 1 reports experiments at the Pennsylvania Station, covering 
three seasons, in which comparable lots of cows were kept in an open 
shed and in an ordinary "bank" barn. It was found that the milk 
yield of both was similarly affected by sudden drops of temperature 
but that the milk yield of the exposed group decreased more rapidly 
during the winter than did that of the sheltered group, the difference 
in the average daily yield for the entire season varying from practi- 
cally nothing in 1911-1912 to about three pounds in 1913-1914. It was 
observed that the exposed cows had the keener appetites and con- 
sumed more roughage than did the sheltered animals. Both groups 
maintained good health. The amounts of milk produced per Therm 
of estimated net energy contained in the feed and also per Therm of 
net energy in excess of the estimated maintenance requirement were 
as shown in the following table from which it appears that the pro- 
duction by the sheltered lot was slightly the more economical. 



Table 129. — Milk Yields of Sheltered and Exposed Cows 



Exposed lot 

1911-12 

1912-13 

1913-14 

Average 

Sheltered lot 

1911-12 

1912-13 

1913-14 

Average 



Per Therm 

Net Energy 

of Total 

Feed 




Per Therm 
Net Energy 
in Excess 
of Mainte- 
nance 



Lb. 

2.244 
2.570 
2-515 
2-443 



2.499 
2.825 
2-639 
2.654 



A number of instances have also been reported in which the sub- 
stitution of a single thickness of muslin in cow stables in place of 
glass windows has proved satisfactory. 

1 Penna. Expt. Sta., Rpt. 1013-1914, pp. 183-226. 



488 NUTRITION OF FARM ANIMALS 

On the whole it may be said that such experiments as are on 
record agree with the deductions from physiological data and 
indicate that the need for warm quarters for dairy cows has 
been overemphasized, but are insufficient to establish the 
limits within which stable temperature does not affect yield. 
Much doubtless depends, as Spier points out, upon the previous 
treatment of the cows. Warmly stabled animals carry a sum- 
mer rather than a winter coat and a low temperature seems 
likely to have more effect on such animals than on those grad- 
ually accustomed to it as the weather grows colder. 

Where cows are kept in the stable most of the time the ques- 
tion of temperature is of special interest in its relation to ventila- 
tion. Practically, a cow stable must be warmed in most cases 
simply by the heat derived from the animals themselves and 
a high temperature can be obtained only by means of more or 
less restricted ventilation. If low temperatures can be used, 
more perfect ventilation, with its beneficial effects upon the 
health and vigor of the animals, is possible. 

§ 4. The Utilization of Feed in Milk Production 

The utilization of protein 

584. Meaning of utilization. — The conception of the utiliza- 
tion of protein in milk production as here considered is substan- 
tially identical with that of its utilization in growth already 
discussed (470). It is the ratio of the protein contained in 
the milk to the least amount of feed protein which is required 
to produce it under the most favorable conditions. 

585. Surplus protein katabolized. — While it is evident that 
milk production requires a liberal supply of protein in the ration, 
the amount actually secreted in the milk is determined pri- 
marily by the individuality of the animal, precisely as is the 
storage of protein in the case of the growing animal. It is not 
possible to increase at will the amount of protein secreted in 
the form of milk by increasing the supply of protein in the feed. 
While it appears to be true that the activity of the milk glands 
can be stimulated somewhat by an abundant protein supply 
(599) , it is nevertheless true that the animal produces an amount 
of milk determined essentially by its capacity and any surplus 
of protein over that necessary for this purpose is katabolized 



MILK PRODUCTION 



489 



just as is the case with a surplus supplied to a young animal, or 
for that matter to a mature animal. Feed protein is substan- 
tially a supply of material and not a cause of production. 

This is strikingly illustrated in experiments by Jordan x in which 
the protein supply of two cows, beginning with a liberal amount, was 
gradually diminished to about one-half and then gradually increased 
again to the original quantity. The following table shows the aver- 
age nitrogen balances of Cow No. 12 of the second series of experi- 
ments, the daily results being grouped into periods as indicated. 

Table 130. — Average Daily Nitrogen Balance of Cows 



Jan. 30-Feb. 6 
Feb. 6-Feb. 16 
Feb. 16-Feb. 26 
Feb. 26-Mar. 8 
Mar. 8-Mar. 18 
Mar. 1 8-Mar. 28 
Mar. 2 8- Apr. 7 
Apr. 7-Apr. 14 



No. OF 


Nitrogen 


Nitrogen 


Nitrogen 


Days 


Digested 


of Milk 


of Urine 




Grams 


Grams 


Grams 


7 


186.6 


81.7 


87.O 


10 


185.2 


81.4 


87-5 


10 


161.6 


77-5 


81.9 


10 


130.8 


74.0 


56.5 


10 


117. 2 


66.6 


43-7 


10 


I43.6 


69.6 


61.8 


10 


I7I-4 


71.6 


89.2 


7 


185.7 


71.9 


104.4 



Gain by 
Body 



Grams 
+ 17-9 
+ 16.3 
+ 2.2 
+ 0.3 
+ 6.9 
+ 12.2 
-f- 10.6 
+ 9-4 



The yields decreased in quite a normal way with the advance in 
lactation, the yield of protein, like that of total milk solids, diminish- 
ing, while the percentage of protein in the latter remained about the 
same. On the low protein rations of the middle periods there seems 
to have been some falling off in the amount of milk protein produced 
in comparison with what might have been expected on an unchanged 
ration, but the difference is small except in one or two periods in which 
the protein supply reached the lowest limit. Aside from this, the 
principal effect of the variations in the amount of digestible protein 
supplied was to increase or diminish the amount of nitrogen excreted 
in the urine, which, as the table clearly shows, rose and fell with the 
supply of nitrogen in the food. 

586. Estimates of utilization of protein. — In attempting 
to reach conclusions regarding the utilization of feed protein 
for the production of milk protein, then, it is evidently necessary 
to avoid an excess of protein in the ration, since such an excess 

1 N. Y. (Geneva) Expt. Sta., Buls. 132 (1897) and 197 (1901). 



490 NUTRITION OF FARM ANIMALS 

is subject to rapid katabolism, so that high protein rations will 
necessarily show a low apparent utilization of the protein for 
milk just as they do for growth (468) . On the other hand, too 
small a supply of protein may cause the tissue proteins of the 
body to be mobilized and utilized as a source of milk protein so 
that a direct comparison of feed protein and milk protein would 
give too high a result. To determine the utilization of feed 
protein, therefore, it is necessary, while maintaining a sufficient 
energy supply, to reduce the protein content of the ration 
as nearly as possible to that which is just sufficient to prevent 
a loss of body protein and then to compare the feed protein 
minus the maintenance requirement with the milk protein. 

Such an experiment obviously requires a determination of 
the nitrogen balance of the animal, and relatively few of the 
reported investigations on milk production include such a 
determination, while in none yet reported has the sufficiency 
of the energy supply been demonstrated by means of respira- 
tion experiments. There are, however, a not inconsiderable 
number of experiments on record in which the live weights of 
the animals have been well maintained and in which amounts 
of digestible protein but little greater than those found in the 
milk plus those estimated to be necessary for maintenance have 
been adequate for the production of at least moderate amounts 
of milk without drawing on the body protein. 

Naturally an exact balance of the income and outgo of nitrogen 
will rarely be secured. In most cases it is necessary to compare the 
feed protein with the algebraic sum of the milk protein and the gain 
or loss of body protein, the comparison being more nearly correct as 
the latter factor becomes smaller. 

Table 131 shows the computed utilization of the protein 
of a number of low protein rations, the daily maintenance 
requirement of crude protein being estimated as 0.6 pound per 
1000 pounds live weight in direct proportion to the latter. It 
includes the experiments by Jordan upon the sources of milk 
fat, the results of one of which as regards protein have just been 
cited, an experiment by Hayward x the results of which as 
regards the nitrogen balance are still unpublished, the ex- 
tensive experiments upon the minimum protein requirements 

1 Penna. Expt. Sta., Rpt. 1901-1902, pp. 314 to 396. 



MILK PRODUCTION 



491 



Table 131. — Utilization of Protein in Milk Production 







Nitro- 


Esti- 


Re- 


Nitrogen Utilized 








gen Di- 


mate 


MATXTQ 






Per- 
cent- 




Pe- 


gested 


for 


FOR 


In 


In 


Total 




riod 




Main- 
te- 
nance 


Pro- 
duc- 
tion 


Milk 


Body 
Gain 




age 
Util- 
iza- 
tion 






Grams 


Grams 


Grams 


Grams 


Grams 


Grams 




Jordan 


















Experiments of 189/ 


4 


65-5 


37-9 


27.6 


35-6 


- 3-5 


32.I 


116 


Experiments of iqoj 


5 


117. 2 


S2.3 


64.9 


66.6 


6.9 


73-5 


113 


Hayward 






• 












Cow Cena . . . 


3 


68.8 


36.8 


32.0 


33-7 


— 2.1 


31.6 


99 


Copenhagen Lab- 


















oratory 


















• 


4 


82 


32 


50 


63 


- 16 


47 


94 


Cow 10 . . . 


5 


80 


32 


48 


60 


— 12 


48 


100 


' 


6 


96 


32 


64 


62 


— 2 


60 


94 


Cow 23 . . . 


4 


81 


35 


46 


59 


- 9 


5o 


109 




5 


83 


35 


48 


57 


- 15 


42 


87 


f 


4 


87 


30 


57 


56 


— 2 


54 


95 


Cow 53 • • • \ 


5 


67 


30 


37 


45 


- 13 


32 


86 


1 


6 


91 


30 


61 


49 


+ 3 


52 


85 




4 


92 


32 


60 


63 


- 5 


58 


97 


Cow 68 . . . 


5 


80 


32 


48 


58 


- 16 


42 


88 




14 


81 


32 


49 


5o 


— 2 


48 


98 


f 


4 


85 


32 


53 


52 


— 1 


5i 


96 


Cow 58 . . . J 


5 


64 


32 


32 


45 


- 13 


32 


100 


1 


6 


93 


32 


61 


47 


+ 6 


53 


87 




3 


92 


30 


62 


65 


- 16 


49 


79 


Cow 68 . . . i 


4 


68 


30 


38 


59 


- 26 


33 


87 




5 


66 


30 


36 


58 


- 23 


35 


97 


L 


6 


92 


30 


62 


59 


- 4 


55 


87 




4 


124 


33 


9i 


83 


- 17 


66 


73 


Cow 125 .. . 


5 


123 


33 


90 


83 


— 12 


7i 


79 




6 


142 


33 


109 


79 


+ 4 


83 


76 


. 


7 


148 


33 


ii5 


79 


+ 7 


86 


75 


Kellner 


















CowE . . . | 


4 


96 


35 


61 


57 


+ 1 


58 


95 




5 


99 


35 


64 


61 


+ 1 


62 


97 



492 NUTRITION OF FARM ANIMALS 

of dairy cows carried on at the Laboratory for Agricultural 
Research in Copenhagen l and unpublished respiration experi- 
ments by Kellner. 2 The experiments of Hart and Humphrey 
mentioned in the next paragraph, when computed in the same 
way, also show a high percentage utilization of the digested 
protein, although the gains and losses of body protein are 
relatively so considerable as to disturb the comparison. 
Haecker's low protein rations in 1902-3-4-5, as noted on a 
subsequent page (602), seem to afford another example of the 
high utilization of feed protein. 

While too much weight should not be attached to the results 
of comparisons like the foregoing, especially since they include 
a more or less uncertain estimate of the protein requirement 
for maintenance, they nevertheless seem to indicate beyond 
reasonable doubt that on low protein rations the protein of at 
least some feeding stuffs may be converted into milk protein 
without any very large loss. 

587. Relative values of proteins for milk production. — The 
considerations advanced in preceding chapters (400, 465) regard- 
ing the relative values of different proteins for maintenance and 
for production render it altogether probable that they also differ 
in value as sources of milk protein. No experiments on this 
point have as yet been reported, but Hart and Humphrey 3 in 
two series of experiments on cows have compared the mixed 
proteins of maize, wheat, gluten feed, oil meal and distillers' 
grains with proteins prepared from milk (784), using maize 
stover and silage as roughage. They found the average per- 
centage of the resorbed nitrogen which was recovered in the 
milk yield plus the gain (or minus the loss) of the body protein 
to be 

Skim milk powder 59 % 

Casein 59% 

Maize 40% 

Wheat 36% 

Gluten feed 45% 

Oil meal 61% 

Distillers' grains < 60% 

1 Denmark-Beretning fra den Kgl. Veterinear of Landbohojskoles Laboratorium 
for landokonomiske Forsog. 6ode, 1906, and 63de, 1907, Kobenhavn. Translated 
by Mallevre, Society de l'Alimentation Rationale du Betail. Compte Rendu de 
ueme et i2eme Congres. 

2 Die Ernahrung der landw. Nutztiere, 6th Ed., 1912, p. 551. 

3 Jour. Biol. Chem., 21 (1915), 239; 26 (1916), 457. 



MILK PRODUCTION 493 

If the probable requirement for protein maintenance be 
deducted from the total resorbed nitrogen, the utilization of 
the remaining protein, calculated as in the experiments of the 
previous paragraph, was notably higher, approaching or reach- 
ing 100 per cent in several instances. 

The differences observed were largely due, however, to fluc- 
tuations in the gain or loss of body protein, the formation of 
milk protein being quite uniform from period to period, and 
this fact seems to render the results of somewhat questionable 
relevance as regards the special question of comparative values 
as sources of milk protein, although they do show marked 
differences in total efficiency. 

The utilization of energy 

588. Net energy values for milk production. — The net 
energy value of a feeding stuff or ration for milk production is 
identical in conception with that for fattening (448) or for 
growth (472) already considered. It is that part of the feed 
energy supplied in excess of the maintenance requirement which 
is recovered in the product. For example, if a cow produces 
per day 20 lb. of four per cent milk, containing (604) 336 
Cals. of energy per pound, the total of 6720 Cals. would be the 
net energy value which must be supplied in the ration in ad- 
dition to that required for maintenance. 

As pointed out in Chapter VIII (371), it cannot be assumed 
that the net energy values for maintenance, fattening or growth 
apply to milk production, but the values for the latter purpose 
must be determined by direct experiment. As yet, very scanty 
data are available on this point, the only results yet reported 
being three contained in a brief preliminary paper by Kellner. 
589. Complete energy balances. — Kellner l reports the 
nitrogen, carbon and energy balances, determined as in his ex- 
periments on oxen, of three cows receiving mixed rations and 
varying considerably in their milk yield. By the method de- 
scribed in Chapter XVII (768-772), it is estimated that the net 
energy values of the rations and the percentage utilization of 
their metabolizable energy for fattening would be : — 

1 5 ter Internat. Kongress fur Milchwirtschaft, 191 1. 



494 



NUTRITION OF FARM ANIMALS 





Starch 
Values 


Equivalent 
Net Energy l 


Net Energy 
as Percentage 
of Metaboliz- 

able Energy 


Cow A 


Kgs. 

6.96 
6.13 

4.84 


Therms 

16.400 

14-443 
11.403 


% 

48.02 

46.35 
43-81 


Cow C 


Cow E 





Estimating the maintenance requirements of the animals 
from their live weights on the basis of his average results on 
the maintenance of oxen (381), Kellner obtains the following 
energy balances showing a considerably higher utilization for 
milk production than that computed for fattening. 

Table 132. — Energy Balances of Dairy Cows 





Cow A 


Cow C 


Cow E 


Income 


Therms 


Therms 


Therms 


In feed .... 


63.309 


59.096 


46.536 


Outgo 

In feces and urine . 
In methane . . . 


25-353 
3-803 


23.783 
4.149 


16.996 
3.5o8 


Total .... 


29.156 


27.932 


20.504 


Metabolizable 








Estimated mainte- 


34-153 


31.164 


26.032 


nance . . . 


10.114 


n.303 


10.586 


Available for pro- 








duction . . . 


24.039 


19.861 


15.446 


Production 








Milk 

Body fat and 


13.907 


10.617 


8.919 


protein . . . 


1.782 
15.689 


2.447 
13.064 


O.928 


Total .... 


9.847 


Utilization of metab- 


% 


% 


% 


olizable energy . . 

Computed utilization 

for fattening . . 


65-3 
48.0 


65.8 
46.4 


63.8 
43-8 



l i Kilogram starch value = 2.356 Therms net energy. 



MILK PRODUCTION 



495 



The percentage utilization in milk production alone may also 
be approximately estimated from Kellner's figures by sub- 
tracting from the metabolizable energy available for production 
the amounts estimated to be required for the production of the 
observed gain of body tissue. The results of this calculation 
are shown in the following table. A similar computation by 
Kellner based on his estimated starch values gives substantially 
the same results. 

Table 133. — Utilization of Metabolizable Energy in Milk Pro- 
duction 



Metabolizable energy 
Available for total 
production . . 
Required for body gain 

Available for milk 

production . . 

Recovered in milk . 

Utilization . . . 



Cow A 



24.039 Therms 
u 
3-7H 

20.328 " 
13.907 

68.41 % 



Cow C 



19.861 Therms 
5-279 » 

14.582 " 
10.617 " 
72.80% 



Cow E 



15.446 Therms 
2.118 " 



13-328 " 

8.919 " 
66.91 % 



590. Partial energy balances. — Partial energy balances of 
two cows which made but slight gains in live weight are re- 
ported by Jordan, 1 the maintenance requirement being esti- 
mated from the live weight and the excretion of methane com- 
puted from the digestible carbohydrates. Assuming that there 
was no gain or loss of fat or protein by the body, the following 
comparisons can be made : — 

Table 134. — Utilization of Metabolizable Energy in Milk Pro- 
duction 





Cow 10 


Cow 12 




Period 1 


Period 2 


Period 3 


Metabolizable energy . . 
Estimated maintenance . 


27.320 Therms 
10.152 "" 


32.118 Therms 

13.846 " 


31.718 Therms 
13.846 " 
17.872 " 
10.169 " 
56.90% 


30.335 Therms 
13.846 *' 


Energy in milk .... 


17.168 " 
8.4S1 " 
49-23% 


18.272 " 
11. 176 " 
61.16% 


16.489 " 
10.547 " 
6396% 



1 N. Y. (Geneva) Expt. Sta., Bui. 197, pp. 24-32 and 20th Rpt. (1901), p. 29. 



496 nutrition of farm animals 

Eckles * has likewise determined partial energy balances of 
ten milking cows for an entire year on rations just sufficient to 
maintain their live weight. In these experiments the percentage 
digestibility of the rations is computed for eight of the cows on 
the basis of results obtained in digestion trials on five of the 
animals, while the maintenance requirement of all but one of the 
cows was determined in live weight experiments after the cows 
were dried off, with the results reported in Chapter VIII (381). 

Estimating the metabolizable energy of the rations at 3.7 
Therms per kilogram of digestible organic matter (753) and com- 
puting the results, exactly as in Jordan's experiments, on the 
assumption of no gain or loss by the body, the following values 
for the percentage utilization in milk production are obtained. 

Table 135. — Percentage Utilization of Metabolizable Energy in 

Milk Production 

Cow No. 206 63.36 % 

Cow No. 304 67.60% 

Cow No. 400 66.90% 

Cow No. 43 5 J -36% 

Cow No. 62 72.82% 

Cow No. 4 60.24% 

Cow No. 27 62.89% 

Cow No. 63 5o-35% 

Average 61.94% 

Haecker, 2 in discussing the results of extensive experiments 
with the dairy herd of the Minnesota Experiment Station, has 
compared the digestible nutrients of the feed and the solids of 
the milk by reducing both to their carbohydrate equivalent. 3 
Subtracting the estimated maintenance requirement from the 
total carbohydrate equivalent (" nutriment ") of the feed, he 
finds that of the remainder from 50.25 per cent to 66.22 per 
cent was recovered in the milk, the general average for nine 
years being 54.65 per cent, while the live weights of the cows 
were in general maintained. This seems to indicate a decidedly 
lower utilization of energy than that computed in Kellner's, 
Jordan's and Eckles' experiments. It must be noted, however, 

1 Mo. Expt. Sta., Research Bui. 7. 

2 Minn. Expt. Sta., Bui. 140 (1914), p. 45. 

3 The fat of the feed is multiplied by the factor 2.2 and that of the milk by 2.25 
and the product added to the carbohydrates and protein. The sums, which are 
called " nutriment," are, of course, approximately proportional to the energy con- 
tent of the milk and the metabolizable energy of the feed respectively. 



MILK PRODUCTION 497 

that the digestibility of the rations in Haecker's experiments 
was estimated from average figures which, according to Eckles' 
results (722), are probably too high for cows in milk, although 
on the other hand Haecker's estimate for the maintenance re- 
quirement also seems high. 

591. Net energy values for milk probably greater than for 
fattening. — A comparison of Kellner's results (589) with those 
obtained by the same author l and by Armsby and Fries 2 for 
the utilization of metabolizable energy in either maintenance, 
growth or fattening seems to indicate clearly that the net 
energy values for milk production are distinctly higher than 
those for the latter purposes, although no direct comparisons 
on the same feeding stuff or ration can be made; 

Both Jordan's and Eckles' results tend to confirm this con- 
clusion, which is further strengthened by the fact, to which 
Eckles calls attention, that with one exception the actual energy 
content of the milk in his experiments was greater than the net 
energy value available in the ration producing it as computed 
by the use of Kellner's factors. 

Unfortunately, no results upon the net energy values of 
single feeding stuffs or nutrients for milk production have yet 
been reported, so that it is impossible at present to make any 
exact quantitative comparisons. 

592. Cause of higher net energy values for milk production. 
— The apparently higher net energy values for milk produc- 
tion as compared with tissue production may be plausibly as- 
cribed to the difference in the composition of the products. 
As shown in Chapters X and XI, the organic matter of the in- 
crease in fattening consists chiefly of fat (441-443) and even in 
the case of growth fat makes up a considerable proportion of it 
(458) except in extreme youth. In average milk, on the com- 
trary, protein and milk sugar constitute two-thirds of the total 
organic matter and carry over one-half of the total energy. 

It seems not improbable that the conversion of digestible 
protein into milk protein, or of digestible carbohydrates into 
milk sugar, may involve a comparatively small expenditure 
of energy as compared with the synthesis of fat from carbo- 
hydrates or protein. If such be the case, the organic matter 

1 Landw. Vers. Sta., 53 (iqoo), i. 

2 Jour. Agr. Research, 3 (1915), 435; 7 (1916), 379. 

2 K 



49 8 



NUTRITION OF FARM ANIMALS 



of the milk would retain a larger percentage of the chemical 
energy of the digestible matter from which it was formed than 
would the increase of body tissue which that same digestible 
matter could produce. 

593. Computation of equivalent net energy values for fat- 
tening. — Let it be assumed that the digestible protein and 
carbohydrates of the feed may be converted into the corre- 
sponding compounds of milk without loss and that the expendi- 
ture of energy in the production of milk fat from carbohydrates 
is the same as that observed by Kellner (769) for the production 
of body fat. Then each gram of protein or carbohydrates in 
the milk would require the supply in the feed of one gram of 
digestible protein or carbohydrates respectively, while each 
gram of milk fat if manufactured from carbohydrates would 
require about 3.9 grams of the latter. 

The corresponding amounts of energy recovered in milk 
production and in fattening respectively would, according to 
the foregoing assumptions, be as follows : — 

Table 136. — Computed Energy Recovered in Milk Production and 

in Fattening 



Supplied in Feed 



1 gram protein 

1 gram carbohydrates 

3.9 grams carbohydrates 



Produced in Milk 



1 gram protein 

1 gram carbohydrates 

1 gram fat 



Energy 

Recovered 

in Milk 



5.7 Cals. 
4.1 Cals. 
9.23 Cals. 



Energy 
Recovered 
in Fatten- 
ing l 



2.24 Cals. 
2.37 Cals. 
9.23 Cals. 



On this basis, it is easy to compute approximately the amount 
of net energy for fattening which would be required for the 
production of a given amount of milk of known composition. 
Thus average four per cent milk, according to Table 144 (604), 
contains 3.08 per cent of protein, 4.85 per cent of carbohy- 
drates and 4.0 per cent of fat. The actual amount of energy 
contained in a pound of such milk would be 336 Cals., while 
the amount of energy which would have been recovered from 
the same feed if used for fattening would have been only 252 
Cals. Conversely, an amount of feed containing 252 Cals. of 
net energy as computed from the results of fattening experi- 

1 Kellner's factors. 



MILK PRODUCTION 



499 



ments would suffice to support the storage of 336 Cals. of 
energy in four per cent milk. The method of computation is 
shown in the following table. 

Table 137. — Energy Recovered in Four Per Cent Milk and in 

Fattening 



Protein . . 
Carbohydrates 
Fat ... 



Total per 100 grams 
Total per pound . 



Energy Recovered in 
Milk 



5.7 X 3-08 = 17.5 Cals. 
4.1 X 4.85 = 19.8 Cals. 
9.23 X 4.00 = 36.9 Cals. 

74.2 Cals. 
336 Cals. 



Equivalent Energy Re- 
covered in Fattening 



2.24 X 3.08 = 6.9 Cals. 
2.37 X 4.85 = 1 1-5 Cals. 
9.23 X 4.00 = 36.9 Cals. 

55.3 Cals. 
252 Cals. 



594. Kellner's results. — Confirmation of this hypothesis 
is afforded by the results of Kellner's respiration experiments 
(589). In substantially the way just outlined, Kellner com- 
putes that while the actual chemical energy of the milk solids pro- 
duced by his cow A was 13.907 Therms, this was equivalent to 
only 10.367 Therms of net energy value for fattening, and there- 
fore, that a ration supplying this amount in excess of that re- 
quired for maintenance and body gain should be sufficient to 
support the observed milk production. For the three cows for 
which results are reported, the requirements for net energy as 
thus computed compared with the estimated net energy values 
of the rations were as follows : — 

Table 138. — Net Energy Values for Fattening in Kellner's Ex- 
periments 



Total in ration 

Required for maintenance 

Required for body gain 

Available for milk production . . . . 
Computed requirement for milk produc- 
tion , 



Cow A 


Cow C 


Therms 
16.400 

4-594 
n.806 

1.782 

10.024 
10.367 


Therms 

14-443 
5-137 
9.306 
2.447 

6.859 
6-975 



Cow E 

Therms 

11.403 

4.806 

6-597 
.928 

5-669 
6.079 



500 'NUTRITION OF FARM ANIMALS 

The amounts of net energy actually available for milk pro- 
duction correspond quite closely with the amounts computed 
to be required according to the foregoing assumptions, and 
Kellner states that this was also the case in a considerable 
number of his unpublished experiments, although in others, 
especially those in which a surplus of feed was given, the agree- 
ment was far from being so good, the difference in one case 
reaching 24 per cent. 

Quite in harmony with the general conclusions of the fore- 
going paragraphs is the statement by Eckles * that in his ex- 
periments " A therm of energy in the feed produced more energy 
in milk when the per cent of fat was low than when it was high. 
Apparently a given amount of feed is more efficient when used 
to produce milk medium to low in fat. It appears from this 
that the production of fat is a greater tax upon the animal than 
is the production of other constituents of the milk carrying 
equal energy value." 

§ 5. Feeding for Milk Production 

595. Feeding a secondary factor. — As has already been 
urged, the feeding of a milking animal is in a certain sense a 
secondary factor in dairying. The possibilities of successful 
milk production depend primarily upon the capacity of the 
animals as milk producers and upon the maintenance of such 
an environment as will give free play to this capacity. Feed, 
on the other hand, while equally necessary, is after all essentially 
the supply of raw material upon which the animal mechanism 
works and cannot greatly stimulate production, though it may 
limit it for lack of material. 

The same thing is substantially true, of course, of all forms 
of productive feeding, but it is especially the case in the feeding 
of dairy animals for the reason already noted (558), that it is 
the product of a single gland and not a general increase of body 
tissue which is desired. Improper rations, therefore, may in 
this case not only limit the total production but, even if suffi- 
cient in quantity, may if deficient in quality deflect production 
from milk to fattening, or possibly to greater muscular activity, 
and thus fail to utilize fully the milk-producing capacity of the 

1 Loc. cit., p. 137. 



MILK PRODUCTION 501 

animals. Feeding, therefore, while in a sense a secondary 
factor is nevertheless an important one. 

596. Feed requirements. — Regarded solely as a source of 
material for the formation of milk, the daily ration must, of 
course, contain an adequate amount of protein and ash and 
a quantity of non-nitrogenous nutrients sufficient to furnish 
material for the manufacture of the non-nitrogenous ingredi- 
ents of the milk, while it must also supply enough energy for 
the physiological activities of the body, including maintenance 
and the energy expended in the processes of milk formation. 

In addition to this, however, there must be taken into con- 
sideration the possibility of the presence or absence in the feed 
of substances which may have a specific effect on the milk 
gland, either by stimulating or depressing its action as a whole 
or by affecting qualitatively the character of its action and so 
the composition of the milk. There is, of course, a possibility 
of such specific effects in other forms of production, but it is 
most obvious in milk production for evident reasons and has 
been most studied in that connection. 

Protein requirements for milk production 

597. Milk rich in protein. — The physiological purpose of 
milk production is, of course, to support the growth of the young. 

The essential feature of growth, however (462), is the pro- 
duction of new protein tissue, which, in the suckling animal, 
is relatively rapid, and in order to support this growth the milk 
must contain protein in amount more or less proportional to 
the rate of growth of the species. Cow's milk is decidedly 
protein in character, the ratio of protein to non-nitrogenous 
ingredients corresponding roughly with that of the increase 
made by an animal three months old (556) . Moreover, in the 
case of the cow, man has been able to increase greatly the natural 
milk-producing capacity, with, of course, a corresponding in- 
crease in the total amount of milk protein formed. Even the 
moderate daily yield of 20 pounds of milk of average composi- 
tion contains over 0.6 pound of protein, while the extraordinary 
yields of champion cows contain several times this amount. 

598. Minimum protein requirement. — Just as in the case of 
growth, it is evident that the least amount of digestible protein 



502 NUTRITION OF FARM ANIMALS 

which can possibly meet the requirements of the milk-producing 
animal is the quantity required for the maintenance of the body 
protein plus the actual amount of protein contained in the milk 
yielded. For example, if a iooo-pound cow is to produce daily 
25 pounds of milk containing 3.2 per cent of total protein, 
it is evident that her ration must contain in digestible form 
at least the 0.8 pound of protein contained in the milk plus 
the approximate 0.6 pound presumably required for body 
maintenance, or a total of approximately 1.4 pounds. A less 
supply than this must evidently result either in a falling 
off in the milk yield or in a conversion of body protein into 
milk protein. 

How much more than this minimum amount must be sup- 
plied by an adequate ration will depend upon the percentage 
utilization of the feed protein in the sense already discussed in 
§ 4 of this chapter (584-586), i.e., upon the proportion of it 
capable of conversion into milk protein. Thus in the illustra- 
tion just employed, if 80 per cent of the surplus feed protein 
can be utilized the protein requirement would be 1 .0 pound for 
milk production plus 0.6 pound for maintenance, or 1.6 pound 
instead of 1.4 pound. The case is parallel with that of the 
protein requirement for growth discussed in Chapter XI (484- 
491) and in both instances the experimental data available are 
insufficient for a final conclusion, although the probabilities 
appear to indicate the possibility of a high percentage utilization 
under favorable conditions. 

599. Protein as a stimulus to the milk glands. — The fore- 
going considerations do not, however, exhaust the subject. In 
them it has been tacitly assumed that the amount of milk protein 
manufactured by the milk glands is substantially fixed. It 
seems well established, however, that in addition to furnishing 
material for the manufacture of milk protein, the nitrogenous 
matter of the feed may act to some extent as a stimulus to the 
glands, causing a more active secretion not only of protein but 
of all the milk solids. In other words, it would appear that a 
greater or less surplus of protein over the amount indicated by 
calculations like the foregoing is necessary if it is desired to take 
full advantage of the milk-producing capacity of the animal or 
to delay as much as possible the natural shrinkage in milk due 
to advancing lactation. 



MILK PRODUCTION 503 

That such is the case has long been taught, but many of the 
early experiments upon which this teaching was based are 
inconclusive in that they relate to the effect of adding protein- 
rich feeding stuffs to relatively light rations low in protein. 1 
The total digestible matter (energy supply) as well as the protein 
in the rations was thus increased, sometimes by a considerable 
amount, the quality of the protein sometimes improved, 
and the proportions of the ash ingredients more or less altered, 
while the possibility of the presence in the added feed of specific 
stimulating substances (617-621) must be reckoned with. It is 
illogical, therefore, to ascribe the beneficial effect entirely to 
the increase in digestible protein, although this was doubtless 
one of the factors. 

Jordan's investigations. — Of more recent investigations in 
which these sources of uncertainty were largely avoided those 
of Jordan, some of the results of which as regards the utilization 
of protein have already been cited (585) , afford a good example 
and may serve to illustrate the general method of such experi- 
ments. Beginning with a ration fairly high in protein, the 
proportion of this nutrient was gradually reduced to a com- 
paratively low figure and then gradually increased again to the 
original amount by an exchange in the rations between a nearly 
pure protein (wheat gluten) and either maize or rice meal. 
The total digestible matter was thus kept practically constant 
while the probability of any specific effect was reduced to a 
minimum. 

The actual yields of total milk solids and of milk protein in 
the several periods are recorded in Table 139 and together 
afford a fairly accurate measure of the amount of production. 
Before drawing conclusions as to the influence of the varying 
protein supply, however, it is necessary to take account of the 
natural shrinkage in milk. Assuming that the rate of falling 
off in milk due to advancing lactation, as shown by the differ- 
ence between the first and last periods, was uniform (571), 
the actual yields of solids and of protein as compared with 
those which would have been anticipated had the feed re- 
mained unchanged, were as follows : — 

1 Compare Wolff's summary in Ernahrung der landw. Nutztiere, 1876, pp. 500- 
55o. 



5°4 



NUTRITION OF FARM ANIMALS 



Table 139. — Influence of Protein Supply on Milk Production 
(Results per day and head) 





Period 


Crude 
Pro- 
tein 
Di- 
gested 


Yield of Milk 
Solids 


Yield of Milk 
Protein 


Gain 

of 

Body 




Com- 
puted 


Ob- 
served 


Com- 
puted 


Ob- 
served 


Pro- 
tein 






Lb. 


Lb. 


Lb. 


Lb. 


Lb. 


Lb. 




1 


1.70 


2.72 


2.72 


0.64 


O.64 


+ 0.03 




2 


1.42 


2-59 


2.28 


O.62 


O.62 


+ 0.05 


Experiment of 1897 


■ 3 
4 


I.85 

0.90 


2.49 
2.38 


2.22 
I.87 


0.60 
O.58 


o-59 
0.49 


+ 0.40 
- 0.05 




5 


0.41 


2. 24 


I.67 


0.56 


0.44 


-0.43 




1(5 


1.58 


1.96 


I.96 


O.51 


0.51 


+ 0.46 




1 


2-57 


4-55 


4-55 


1. 12 


1. 12 


+ 0.25 




2 


2.63 


4.41 


4.20 


I. IO 


1. 12 


+ 0.30 




3 


2.20 


4.28 


4.02 


I.08 


1.07 





Experiment of 190 1 


4 
' 5 


1.80 
1.60 


4.14 
4.01 


3-77 
3-5o 


I.06 
I.05 


1.02 
0.92 




+ 0.08 




6 


1 1.98 


3.87 


3-57 


I.03 


0.96 


+ 0.17 




7 


2-35 


3-73 


3-65 


I. OI 


0.99 


4-O.I3 


- 


I 8 


2-55 


3.60 


3.60 


O.99 


0.99 


4- 0.12 



Although the low protein rations were able to support a con- 
siderable milk production without causing the body protein to 
be drawn upon materially, nevertheless, a more liberal supply 
of digestible protein was accompanied by a distinctly greater 
production of both total milk solids and milk protein. 

M or gen's investigations. — The extensive investigations of 
Morgen and his associates l upon milk production by sheep 
include a large number of trials in which an exchange between 
comparatively pure protein on the one hand and starch or oil 
on the other was made in the rations. The results, therefore, 
afford valuable data regarding the influence of the protein 
supply as distinguished from the possible effects of associated 
factors. In nearly all instances the ration of the low protein 
period contained a considerable surplus of digestible protein 
above the total of milk protein plus maintenance protein. In 
the following table, computed by the writer, the experiments 

1 Landw. Vers. Stat., 61 (1904), 1 ; 62 (1905), 251 ; 64 (1906), 93; 66 (1907), 63. 



MILK PRODUCTION 



505 



have been grouped according to the amount of this surplus, and 
the average percentage increase in the yield of milk solids and 
of milk fat which resulted from an increase of the feed protein 
has been computed for each group. 

Table 140. — Influence of Protein Supply on Milk Production 





Num- 
ber OF 
Ex- 
peri- 
ments 


Surplus l Protein as Per 
Cent of Milk Protein 


Percentage In- 
crease of Yield 
on High Protein 
Rations 




In Low Protein 
Rations 


In High 
Protein 
Rations 




Milk 
Solids 






Range 


Average 


Milk 
Fat 






Less than 










Protein substituted 


1 
5 


x 5° 
150-249 


121 
194 


231 
334 


+ 27.4 
+ 7-2 


+ 23.5 
- 7-6 




9 


250-349 


299 


549 


+ 2.1 


— IO.I 




2 


350-449 


411 


525 


+ 8.9 


- 1.3 




2 


4SO-S49 


450 


412 


- 9-6 


- 14-5 




19 

7 


150-249 


214 


348 


+ 12.8 


+ 6.6 


Protein substituted 
for carbohydrates . 


6 
8 
4 


250-349 
350-449 

450-549 


311 

374 
492 


437 
429 
641 


+ 18.9 

+ 7-i 

+ 8.8 


+ 7-1 
+ 5-5 
+ 5-6 




1 


550-649 


637 


742 


+ 25.6 


+ 27.6 




2 


650-749 


669 


534 


+ 69.5 


+ 54-7 




3 


750- 


802 


897 


+ 20.3 


+ 18.4 




3i 





On the whole, Morgen's investigations seem to furnish con- 
clusive evidence of a stimulating effect of protein on milk pro- 
duction. Even when the protein supply already largely exceeded 
the minimum demand, a further addition was in most instances 
followed by a distinct increase in the yield of milk solids and 
usually in that of milk fat. It should be said, however, that a 
respectable minority of the individual experiments failed to 
show this effect. Of the nineteen single trials in which protein 
was substituted for fat, eleven showed an increased yield of 
milk solids and six an increased yield of milk fat. Out of the 

1 Digestible protein minus requirements for maintenance and for growth of wool. 



506 NUTRITION OF FARM ANIMALS 

thirty-one trials in which protein was substituted for carbo- 
hydrates, twenty-six showed an increased yield of milk solids 
and twenty-one an increased yield of milk fat. In thirteen out 
of the entire fifty experiments, therefore, the presence of ad- 
ditional protein failed to cause an increase in the milk solids, 
while in twenty-three trials it failed to produce an increase of 
milk fat. 

600. Effect of protein-rich feeds. — In addition to investiga- 
tions like those noted in the last paragraph, in which the effect 
of an interchange of practically pure nutrients was studied, a 
considerable number of experiments are on record in which an 
enrichment of a ration in digestible protein has been effected 
by an interchange of feeding stuffs, as for example, by the 
substitution of cottonseed meal for maize meal. 

In all these experiments the low protein rations contained, 
with one or two exceptions, a surplus of digestible protein above 
the milk protein plus the estimated maintenance, yet a further 
increase of digestible protein was followed by a larger yield 
of milk per unit of organic matter digested, the increase rang- 
ing from i per cent to 39 per cent. As in the experiments 
described in the previous paragraph, the results appear some- 
what capricious, showing no consistent relation between the 
excess of protein supplied and the relative increase of milk pro- 
duction secured. 

It should be added that in many of these experiments the 
proteins of the low-protein rations consisted to a considerable 
extent of maize protein, which has since been shown to be of 
inferior nutritive value (783). 

601. Protein fed in American practice. — On the basis of 
experiments and observations, Wolff * recommended a standard 
for dairy feeding calling for 2.5 pounds of digestible protein 
daily per 1000 pounds of live weight. Although later modified 
by Lehmann, this standard was for many years almost uni- 
versally accepted on Wolff's authority, supported by the un- 
doubted fact that in many instances the addition of protein-rich 
feeding stuffs to ordinary farm rations materially increased the 
milk yield. Later observations, however, seem to indicate 
that while protein is important the amount necessary in practice 
has been somewhat overestimated. 

1 Die Ernahrung der landw. Nutztiere, 1876, p. 548. 



MILK PRODUCTION 



507 



Woll 1 was the first to make an extensive study of dairy 
practice in the United States as regards the protein supply, 
rinding that very many successful dairymen were using rations 
supplying materially less protein than was called for by Wolff's 
standard. The average of all the rations reported as compared 
with Wolff's standard was as follows : — 

Table 141. — Digestible Matter in Dairy Rations 




Woll's Aver- 
age 



Dry matter . . 

Digestible matter 
Protein . . 
Carbohydrates 
Fat ... . 

Nutritive ratio . 



24.51 Lb. 

2.15 Lb. 
13.27 Lb. 
0.74 Lb. 
i:5-9 



Woll points out that this average, while it does not represent 
any scientific investigation of milk production, expresses the 
results of American feeding experience, and although it does not 
demonstrate either that less protein would not be sufficient or 
that more would not be advantageous, it does afford a safe 
guide for practice, and indicates that rations containing less 
protein than the Wolff standard calls for are probably more 
profitable. 

Somewhat similar observations were reported by Phelps 2 
in 1 89 2-1 893 with the additional feature that in several in- 
stances the rations fed were subsequently modified at the sug- 
gestion of the experimenter and the yield on the new ration 
determined. Phelps recommends a supply of 1.9 to 2.5 pounds 
digestible protein per head according to the productiveness of 
the cow, the amount to be based on the yield of milk rather than 
on the live weight, and believes such rations will give more 
economical production than those containing less protein. 

602. Experiments on herds. — Haecker 3 has reported ex- 
tensive observations and experiments on the protein supply 

1 Wis. Expt. Sta., Buls. 33 (1892) and 38 (1894). 

2 Conn. (Storrs) Expt. Sta., Rpt. 1897, pp. 17-66. 

3 Minn. Expt. Sta., Buls. 71, 79, and 140. 



5 o8 



NUTRITION OF FARM ANIMALS 



of the dairy herd of the Minnesota Station, leading to the con- 
clusion that the Wolff -Lehmann standard calls for unnecessarily 
large amounts of protein. 

During nine years, yields which were regarded as normal and 
satisfactory, either on the basis of total amounts produced or 
of feed consumed per unit of milk, were secured on rations con- 
taining, with the exception of the year 1 895-1 896, about 2 
pounds of digestible protein per 1000 pounds live weight. 1 

During three of these years, comparisons were also made 
between a group of cows receiving about 2 pounds of digestible 
protein per day and 1000 pounds live weight and one receiving 
about 1.5 pounds. In the earlier years the low protein rations 
appeared as efficient as the higher ones, but toward the end of 
the three years the low protein group showed deficient vitality, 
apparently indicating a lack of protein. 

In all nine years, the (estimated) digestible protein in the 
high protein rations supplied a considerable surplus over the 
protein of milk plus maintenance. Estimating the mainte- 
nance requirement of protein at 0.7 per 1000, Haecker makes 
the following comparisons : 2 — 

Table 142. — Protein Supply of Dairy Herd 









Digestible Protein 


Protein 
in Milk 


Available 
Protein 




In Feed 


For Main- 
tenance 


Available 
for Milk 


Protein 
in Milk 


I 894-1 895 . 

1902-1903 . 

I 903-1 904 . 
1904-1905 . 

Average . 
1905-1906 . 
1906-1907 . 
1907-1908 . 
1 908- 1 909 . 

Average . 






Lb. 

2.00 
I.92 
I.97 
1.92 

i-95 

1.63 
1.74 

i-75 
1.86 

1.74 


Lb. 

O.67 
.62 
.64 
.63 
.64 
.60 
.64 
.61 
.66 

•63 


Lb. 

*-33 
1.30 

i-33 
1.29 

i-3i 
1.03 

1. 10 
1. 14 

1.20 

1. 11 


Lb. 
0.814 
•793 
•747 
.769 

.781 
' .772 
.803 
.823 
.828 
.806 


Lb. 

1.63 
1.64 
1.78 
1.68 

1.68 

i-33 
i-37 
i-38 
1-45 
i-38 



1 Bui. 140, p. 43. 



2 Ibid,, p. 54. 



MILK PRODUCTION 



509 



The protein content of the milk from the low protein groups 
is not reported, but an approximate estimate indicates that it 
could not have been much less than the surplus of feed protein 
over maintenance, thus furnishing further instances of an ap- 
parently high percentage utilization of feed protein (586). 
While the indications are that such very low protein rations 
were inadequate, it seems clear that a surplus of 40 or 50 per 
cent of available protein over that contained in the milk was 
ample to support normal production. 

Woll 1 has reported a nine-year series of observations on the 
dairy herd of the Wisconsin Station, the time being divided into 
three periods of three years each, during the first and third of 
which the rations had a nutritive ratio of 1:7, while during the 
second three years it was 1 : 6. The estimated digestible pro- 
tein consumed per day by cows weighing slightly over 1000 
pounds was 

Average of periods A and C 1.76 pounds. 
Average of period B 1.97 pounds. 

Table 143. — Surplus of Available Protein in Herd Rations 



Period A, Low protein . . . . < 
Average 

Period C, Low protein . . . . < 
Average 

f 

Period B, High protein . . . 
Average 



Available 
Protein 



Lb. 

I.03 
1.41 
1. 18 

1. 21 

0.82 
1. 11 
1.07 

1. 00 

1-54 
I.18 
1.22 

i-3i 



Milk 
Protein 



Lb. 
0.72 
0.80 
0.69 

0.74 

0.58 

o-73 

0.76 

0.69 

0.70 

°-59 
0-63 

0.64 



Surplus of 

Available 

Protein 



Per Cent 

43 
76 

_7£ 

63 

41 
52 
41 

45 

120 

100 

94 

105 



1 Wis. Expt. Sta., Research Bui. 13. 



510 NUTRITION OF FARM ANIMALS 

The results for the entire year and likewise for the winter rations 
showed on the whole a somewhat greater and a decidedly more 
economical average production on the smaller supply of pro- 
tein. The protein content of the milk is not stated, but esti- 
mating it at 3.38 per cent and allowing 0.6 pound per 1000 for 
protein maintenance, the approximate surplus of the available 
protein (digestible protein minus maintenance requirement) 
over the milk production in the winter rations was as shown 
in Table 143 in each of the nine years. 

603. Summary. — In view of the great differences between 
individual cows both as to yield and composition of milk, it is 
clear that no one figure can express the protein requirement for 
milk production per day and head, but that it must vary with 
the amount and character of the milk produced. 

It appears to be fairly well established (586) that the digesti- 
ble feed protein of ordinary mixed rations may be converted 
into milk protein without any very great loss and that conse- 
quently a moderate rate of milk production may be maintained, 
at least for a time, on rations furnishing a comparatively small 
surplus of digestible protein over the milk protein plus the 
requirement for maintenance. 

On the other hand, however (599, 600), both experiments with 
pure proteins and those in which an increase in the protein con- 
tent of rations has been secured by the use of protein-rich feeds 
seem to indicate clearly a stimulating influence of excess protein 
on milk production, although in the majority of cases the effect 
was not very large. Contrary to what might have been antici- 
pated, however, an increase in the digestible protein of the ration 
appears to have been on the whole quite as effective with ani- 
mals already on a high plane of protein nutrition, i.e., receiving 
a large surplus over the minimum requirement as with those 
on a much lower level of protein supply. This appears 
with especial clearness in Morgen's experiments on sheep. 
The results therefore fail to indicate the limits within which 
this stimulating effect is manifest or to establish any quantitative 
relation between the surplus protein supplied and the additional 
milk yielded. They afford no basis, therefore, for any estimate 
of the extent to which a stimulation of milk production by means 
of excess protein will be economically profitable under any given 
conditions. 



MILK PRODUCTION 



511 



The experiments by Haecker and by Woll on herds (602) 
seem to justify the conclusion that in commercial milk produc- 
tion in the United States a ration supplying, in addition to the 
maintenance requirement, digestible protein equal to 150 to 
160 per cent of the milk protein yielded is ample in this respect 
to sustain a normal rate of milk production and may be dis- 
tinctly more profitable than a ration richer in protein. It is 
not impossible, however, that when circumstances warrant 
the effort to secure the maximum production possible to the 
animal a more liberal supply of protein would be advantageous. 



Energy requirements for milk production 

604. Energy content of milk. — As in other forms of stock 
feeding, the principal factor in determining the energy required 
in the feed is the amount of chemical energy contained in a 
unit of product. In the case of milk production this factor 
varies through a wide range on account of the large differences 
in composition of milk due to individual and breed differences, 
stage of lactation, etc. 

Haecker l has arranged the results of analyses of 543 samples 
of milk in ten groups according to the fat content. His averages, 
together with the energy content per pound of milk as computed 
by the writer, are as shown in the following table : — 

Table 144. — Composition and Energy Value of Milk 



Number of 


Composition 


Total 


Samples 


Milkings 


Fat 


Protein 


Carbohy- 
drates 


Energy per 
Pound 


47 
55 
57 
116 
103 
89 

39 
24 

13 


658 
770 
798 

1624 

1442 

1246 

546 

336 
182 


% 

2-5 
3-o 

3-5 
4.0 

4-5 
5-o 

5-5 
6.0 

6-5 

7.0 


% 
2-55 

2.68 
2.81 
3.08 
3-27 
3-45 
3-65 
3.82 
4.02 
4.22 


% 

4-45 
4.60 

4-75 
4-85 
4-97 
4.99 
4.92 
4.91 
4.90 
4.84 


Cals. 

253 
278 
306 
336 
365 
390 

415 
440 
467 
492 



1 Minn. Expt. Sta., Bui. 140, p. 51. 



512 NUTRITION OF FARM ANIMALS 

If there were available definite knowledge regarding the net 
energy values of feeding stuffs for milk production, the fore- 
going figures for the total energy of the milk would serve 
as a basis for estimating the net energy supply required for 
the production of a given yield of milk for any one of the 
ten grades, 25 pounds of 4 per cent milk, for example, requiring 
336 X 25 = 8400 Cals. of net energy in the feed. 

605. Equivalent energy values for fattening. — In the ab- 
sence of determinations of the net energy values of feeding stuffs 
for milk production (588) it is impossible to make direct use, in 
the manner just indicated, of the foregoing data regarding the 
energy content of milk. Pending such determinations, however, 
it appears possible to estimate the net energy requirements in 
the feed of dairy cows in another way, viz., by computing from 
the composition of the milk, in the manner already described 
(593), the amount of fattening which is equivalent in energy 
requirement to a unit of milk yield. Thus it was estimated, 
on certain assumptions, that the amount of feed energy required 
for the production of one pound of average 4 per cent milk would, 
if applied to fattening, have produced a gain of only 252 Cals. 
in place of the 336 Cals. actually present in the milk. Accord- 
ingly, a ration containing, in excess of maintenance, 252 Cals. 
of net energy for fattening would have been adequate to pro- 
duce a pound of milk containing 336 Cals. of energy. In 
this way the amount of net energy required for the production 
of one pound of milk of each of the grades included in the 
previous table may be computed. 

By this device of reducing the total energy content of the milk 
to the equivalent amount of net energy for fattening, it appears 
possible to utilize the net energy values of feeds obtained by 
Kellner and others in maintenance or fattening experiments 
as a basis for computing rations for milk. Such a method is, of 
course, provisional, and the basis for it at present is somewhat 
slender, but it seems the best one now available. In its actual 
use for computing rations, however, it appears necessary also 
to take into account the fact shown by Eckles (722) that with 
well-fed cows the digestibility of the rations is on the average 
some 5 per cent lower than the average digestion coefficients 
which are used in computing net energy values. Accordingly, 
the figures for the equivalent energy for fattening as computed 



MILK PRODUCTION 



513 



for the several grades of milk have been increased by 5 per cent, 
giving the following results, which may be used provisionally 
to compute from the figures of Table VII of the Appendix 
the rations required for the production of milk of different 
grades. 

Table 145. — Equivalent Energy Values for Fattening 



Per Cent Fat in Milk 


Equivalent Energy Values per Lb. 
5 of Milk 1 




Cals. 


2-5 


190 


3-o 


214 


3-5 


238 


4.0 


265 


4-5 


291 


5-o 


315 


5-5 


338 


6.0 


361 


6-5 


385 


7.0 


408 



606. Concurrent fattening. — Were all the surplus feed above 
the maintenance requirement applied to milk production, it 
would be a comparatively simple matter to compute the amount 
of feed energy required in a daily ration. Thus, if a cow weigh- 
ing 1000 pounds were capable of producing 25 pounds of 4.5 
per cent milk daily, the net energy required in her ration would 
be computed as follows : — 



For milk production 25 lb. of milk ©291 Cals. 
For maintenance 



7.275 Therms 
6.000 Therms 

13.275 Therms 



Attention has been called several times, however, to the 
fact that in the milking animal at least two forms of production 
are possible, viz., milk and increase of body tissue (fattening), 
only the former of which is usually desired. To these may 
perhaps be added, as a third form of production, a possible 
stimulation of the incidental muscular activity of the animal 
by heavy feeding (609). Evidently if conditions are such that 

1 Including 5 per cent allowance for difference in digestibility. 
2 L 



514 NUTRITION OF FARM ANIMALS 

part of the feed energy is diverted to these other purposes, the 
ration must supply more net energy per pound of milk than 
would be necessary if all the latter were utilized for milk pro- 
duction. 

607. Influence of plane of nutrition. — It appears to be well 
established both by common experience and by direct experi- 
ment that such a diversion of energy from milk production to 
other forms may in fact take place before the maximum capacity 
of the milk glands is reached. On moderate rations, the net 
energy, after satisfying the maintenance requirement, may 
apparently be utilized entirely for milk production. As the 
feed is increased, however, the animal does not continue to 
utilize all the available net energy for milk production up to 
the limit of its capacity and then suddenly begin to utilize any 
surplus for fattening. On the heavier rations the concentration 
of the digested nutrients in the body fluids increases, the organ- 
ism reaches a higher plane of nutrition, and at a point varying 
with different individuals this greater concentration of available 
material causes fattening to begin, which, so to speak, robs the 
milk glands of feed intended for milk production. 

608. Influence of individuality. — The individuality of the 
animal is a most important factor in this connection. With 
cows having an inherited tendency toward fattening, as in the 
so-called beef breeds, this point at which energy begins to be 
divided between milk production and fattening may be reached 
on comparatively light rations. Such animals can be brought 
up to their maximum milk-producing capacity only at the 
expense of a considerable expenditure of feed for concurrent 
fattening and are likely to be unprofitable for dairy purposes. 
On light rations, giving a moderate yield of milk, the mainte- 
nance requirement constitutes too large a proportion of the feed 
cost, while with heavier feeding production is directed too 
largely to fattening. 

With the typical dairy animal, on the other hand, having 
but a slight tendency to fatten, the feed may be increased well 
towards the amount required to support the maximum capacity 
of the milk glands, or in exceptional cases even up to that point, 
without causing any material diversion to fattening. Such 
animals, especially if of large milk-producing capacity, are the 
profitable dairy animals so far as the cost of feed is concerned. 



MILK PRODUCTION 515 

The relations between feed supply, milk production and fatten- 
ing outlined in the foregoing paragraphs have been clearly 
demonstrated in a number of investigations on dairy feeding, 
such as those of Waters, Caldwell and Weld x and of Waters 
and Hess 2 at the Pennsylvania station, those by Woll and 
Carlyle 3 at the Wisconsin station, and especially those by 
Haecker 4 at the Minnesota station. 

609. Stimulation of katabolism. — But while the diminish- 
ing returns obtained from the feed of the dairy cow as its amount 
is increased beyond a certain maximum may be explained in 
part by a diversion of net energy from milk production to fat- 
tening, it seems to be true also that heavier feeding may cause 
a larger proportion of the digested organic matter to be oxidized, 
either as the result of greater muscular activity or by a direct 
stimulation of the katabolic processes. This is especially evident 
in breed tests in which heavy rations have been consumed. 
Striking illustrations of it are afforded by the results of the 
tests of dairy breeds at the Louisiana Purchase Exposition in 
1904 as computed by Haecker 5 and by the extensive comparisons 
of German breeds reported by Hansen. 6 

610. Diminishing returns from feed. — It is evident from 
the foregoing that, with the possible exception of cows of a very 
pronounced dairy type, the maximum yield of milk can be 
secured only at the expense of a simultaneous production of 
more or less body fat and perhaps also of a stimulation of the 
katabolic processes of the body. Consequently, beyond the 
point at which this fattening or stimulation begins, the milk 
production per unit of net energy in the feed must necessarily 
be a diminishing one, and it is clear that the determination of 
the net energy requirements for milk production is to a consider- 
able extent an economic problem. 

Milk will be produced at the least feed (energy) cost per 
pound when the ration is so adjusted as to produce as great a 
yield of milk as is possible without causing fattening. 7 If the 

1 Penna. Expt. Sta., Rpt. 1893, p. 24-36. 2 Ibid., Rpt. 1895, p. 24-55. 

3 Wis. Expt. Sta., 17th Rpt. (1900), p. 37-61. 

4 Minn. Expt. Sta., Buls. 79 and 140. 5 Minn. Expt. Sta., Bui. 106, p. 158. 

6 Landw. Jahrb., 35 (1906), Ergzbd. IV, 147-236; 37 (1908), Ergzbd. Ill, 236- 
410; 2 er Ber. vom Dikopshof (191 1), 210, 430. 

7 It may be presumed that the stimulating effect upon the katabolism occurs 
chiefly in heavy feeding which causes fattening also. 



516 NUTRITION OF FARM ANIMALS 

energy supply is decreased below this point the milk yield will 
tend to fall off while the maintenance requirement remains 
practically constant. The maintenance, therefore, will consume 
a larger percentage of the total feed energy so that, exactly as 
in growth or in fattening, while the net energy requirement 
for the formation of a unit of milk remains approximately con- 
stant, the total net energy necessary to support both main- 
tenance and milk production increases relatively per unit of 
product. 

On the other hand, if the feed is increased so as to cause fat- 
tening or to stimulate katabolism, it is clear that the energy 
requirements per unit of milk produced will be apparently in- 
creased for the reasons already explained. Such an increase in 
the feed cost, however, may be economically justifiable for the 
same reasons as in the case of any form of intensive production. 
In average commercial milk production, it may be doubted 
whether the rations should be made heavy enough to cause any 
considerable fattening, and so far as this is the case, the esti- 
mated net energy values per unit of milk in Table 145 may 
serve as the basis for computing rations. If, however, feed is 
relatively cheap and dairy products high in price, the diminish- 
ing returns due to heavier feeding may still be profitable up 
to a certain point even though more energy per unit of milk 
must be supplied in order to support concurrent fattening, 
while the fact that more or less of the fat stored in the body 
may be utilized for the support of milk production in the early 
stages of the next lactation is also to be considered. 

Fat requirement for milk production 

611. Is fat essential? — It was noted in discussing the func- 
tions of the nutrients (265) and also in connection with the re- 
quirements for growth (498, 499) that the presence in the feed 
of certain fats or of substances associated with them appears to 
be essential to growth. Since milk production is in many re- 
spects analogous to growth it is of interest to inquire whether 
the fats of the feed exert any such specific effect, either on milk 
production as a whole or on the production of milk fat. 

That milk fat as well as body fat may be manufactured in 
the body in large amounts from other nutrients has been shown 



MILK PRODUCTION 517 

beyond question by the experiments of Voit, Kuhn and Fleischer, 
M. Fleisher, Wolff and especially by those of Jordan, 1 while 
the latter investigator demonstrated that milk fat can be 
formed from carbohydrates (553). Jordan's experiments on 
cows, as well as the later ones of Morgen 2 on sheep and goats, 
likewise show that relatively large amounts of milk may be 
produced on rations made up of feeding stuffs very poor in fat 
or from which the larger part of the fat has been extracted. 
It is scarcely feasible to prepare absolutely fat-free rations for 
such animals and the writer is not aware of any experiments on 
milk production with such rations, but it is clear that at most 
but very small amounts of fat can be regarded as indispensable. 
612. Addition of fat to rations. — Experiments in which the 
fat content of ordinary rations has been increased, either by 
the direct addition of fat in one form or another or by the sub- 
stitution of fat for carbohydrates, have given very contradic- 
tory results. An increased percentage of fat in the milk has 
been very frequently observed, sometimes accompanied by an 
increase in the actual yield of fat and sometimes not, while in 
other cases the results have been entirely negative. In many 
instances the experiments are complicated by the fact that the 
fat was simply added to a basal ration, thus increasing the 
total amount of feed. 3 The most recent investigations are 
those undertaken upon a common plan under the auspices of 
the German Agricultural Council at ten German experiment 
stations with, in all, 196 cows, the results of which have been 
reported by Kellner. 4 

The increase in the fat of the rations was effected by the substitu- 
tion of rice feed 5 for rye meal and starch, so that fat replaced an 
equivalent amount of carbohydrates. The results, therefore, in- 
cluded any "specific" effects of these two feeding stuffs, if such there 
were (618). Per 1000 pounds live weight, the fat-poor rations con- 
tained 0.25 to 0.50 pound digestible fat and the fat-rich 0.47 to 1.10 
pounds. 

1 N. Y. (Geneva) Expt. Sta., Buls. 132 (1897) and 197 (1901). 

2 Landw. Vers. Stat., 61 (1904), 1 ; 62 (1905), 251 ; 64 (1906), 93. 

3 Compare Kellner, Die Ernahrung der landw. Nutztiere, 6th Edition, pp. 564-566. 

4 Reichsamt des Innern ; Berichte liber Landwirtschaft, Heft 1 and 2. 

5 According to Hansen rice feed has the specific effect of depressing the fat pro- 
duction, although this effect did not appear manifest in most of these experiments 
nor in those of Fingerling (613). 



5i8 



NUTRITION OF FARM ANIMALS 



Grouping the results regarding the fat content of the milk 
according to the total amount of milk yielded, it appears that 
an increase in the percentage of fat in the milk was in general 
associated with a decrease in the total yield and vice versa. 

Table 146. — Effect of Increasing Fat of Rations 



Experiments At 



Danzig . . 
Bonn . . . 
Pommritz 
Kiel . . . 
Breslau . . 
Triesdorf 
Weihenstephan 
Lauchstadt . 
Darmstadt . 
Jena . . . 
Average . 



Percentage In- 
crease (+) OR 
Decrease (— ) of 
Milk Yield 



- 0.5 % 
" 2.5 % 

- 7-9 % 
+ 0.2 % 

" 3-1 % 
~ 2.3 % 

- 7.1 % 
+ 2.1% 

-6.7% 
+ 0.5 % 

-2.7% 



Percentage In- 
crease (+) OR 
Decrease (— ) 

in Fat Content 
of Milk 



9-8% 
6.6% 

3.3% 
5.o% 
0.3% 
2.6% 
0.6% 
4-8% 

- 1.0% 

- 10.8 % 

- 3-7% 



+ 



+ 



Striking individual differences in cows, however, were ob- 
served. For example, in two of the experiments the range of 
increase or decrease for the individual animals consequent on 
the substitution of fat for carbohydrates was as follows : — 



Table 147. — Influence of Individuality on Effects of Fat Increase 



Experiments at 


Increase (+) or 

Decrease (— ) of 

Milk Yield 


Increase (-(-) or 

Decrease (—) in 

Fat Yield 


Weihenstephan 


Kgs. 
+ 1.85 to — 2.24 
-f 0.22 to — 2.09 


Grams 

+ 53 to - 92 
+ 32 to - 42 



It seems clear from the foregoing results that under the 
average conditions of practice no material advantage can be 
expected from increasing the digestible fat of dairy rations 



MILK PRODUCTION 519 

above 0.4 to 0.5 pound per 1000 pounds live weight, although a 
gain may result with individual cows. 

613. The minimum of feed fat. — On the other hand, the 
extensive investigations by Morgen and his associates on sheep 
and goats, already referred to (599) , have shown that with these 
animals an increase of the fat content of rations exceptionally 
deficient in this ingredient results in most cases in an increased 
yield of milk solids and especially in a specific increase of the 
fat content of the milk. 

The rations consisted of a basis of roughage poor in fat * to which 
various commercially pure nutrients were added. Fat in various 
forms was added to scant basal rations and likewise substituted for 
carbohydrates or protein in heavier rations. Experiments of the latter 
sort, in which the energy content of the rations was kept substantially 
unchanged, are especially convincing. An increase of the fat content 
of the fat-poor rations, either by direct addition or by substitution, 
up to 0.5 to 1.0 lb. per 1000 lb. live weight not only resulted in a 
distinct increase in the yield of milk and of milk solids but likewise 
in an increased percentage of fat in the fresh milk and in the milk 
solids. This specific influence of fat as compared with protein is 
illustrated in Table 140, which shows that while a substitution of 
protein for fat or for carbohydrates increased the yield of solids, 
the yield of fat was decreased in the former case. Fingerling 2 has 
likewise shown that increasing the fat content of a ration by substi- 
tuting a feed rich in fat for one rich in carbohydrates (rice meal in 
place of barley meal) likewise increases the fat yield. 

This specific effect of feed fat on the production of milk fat 
appears to be more marked in the case of sheep and goats than 
in the case of cows. It was observed up to a limit of approxi- 
mately 1.0 pound per 1000 pounds live weight, but above that 
the results were if anything negative, while with cows, as al- 
ready shown, an increase of the digestible fat above 0.4 pound 
per 1000 pounds live weight generally produces little or no 
effect. Morgen ascribes the difference to the greater relative 
production of fat per unit of weight by the smaller animals. 

In ordinary dairy rations fat will not often fall below the 
apparent limit of 0.4 to 0.5 pound. Only when feeds unusually 
poor in fat are used, such as straw or inferior grades of hay or 

1 In. part artificially extracted. 2 Lanclw. Vers. Stat., 64 (1906), 299. 



520 NUTRITION OF FARM ANIMALS 

by-products containing a minimum of fat, may a favorable 
effect upon the yield of milk and its percentage of fat be antici- 
pated from an increase in the supply of digestible fat. 

614. Influence on utilization of energy. — None of the ex- 
periments on the influence of the fat supply upon milk production 
afford any exact data regarding the concurrent gain or loss of 
tissue, since no determinations of the gaseous excreta were made. 
It is impossible, therefore, to determine whether the observed 
effect of the feed fat was brought about by a stimulation of milk 
production at the expense of fattening, i.e., by modifying the 
direction in which the energy of the feed was utilized, or whether, 
under its influence, the metabolism in the milk gland was actu- 
ally effected more economically. 

Ash requirements for milk production 

Practically no data are on record upon which a trustworthy 
estimate of the ash requirements of the dairy cow can be based. 

615. The outgo in the milk. — It is true that the outgo of 
mineral elements in the milk may be determined without special 
difficulty and that reasonably accurate figures are available 
from which it may be estimated. This, however, is but a single 
element in the problem. It became evident in considering the 
ash requirements for maintenance in Chapter IX (421-436) 
and those for growth in Chapter XI (492-497) that neither the 
actual availability of the mineral elements of feeding stuffs 
nor the influence of the amount and quality of the ash supply 
upon the losses in feces and urine has been sufficiently investi- 
gated to permit any satisfactory conclusions as to the influence 
of these factors. 

Kellner * has, however, computed the approximate require- 
ments for calcium and phosphorus from the outgo in the milk. 
Accepting Henneberg's estimate of 71.4 grams of calcium and 
21.8 grams of phosphorus per 1000 kilograms live weight for the 
maintenance requirements, he adds to these three times the 
average amounts found in the milk upon the somewhat ques- 
tionable assumption that only one-third to one-half the feed 
ash is available. Computed for a yield of 20 pounds of milk 
per day by a thousand pound cow, his results are as follows : — 

1 Ernahrung landw. Nutztiere, 6th Ed., p. 595. 



MILK PRODUCTION 52 1 

Table 148. — Estimated Requirements for Milk Production 





Calcium 


Phos- 
phorus 


For production of 20 lb. of milk 


Grams 

32 
29 


Grams 
10 
15 


Total 


61 


25 





616. The supply in the feed. — Kellner states that ordinary 
dairy rations will usually meet the requirements just stated and 
that only in exceptional cases will it be necessary to supplement 
the calcium supply. 

Forbes 1 has shown, however, that rations fully adequate, so 
far as organic nutrients are concerned, to support a considerably 
greater milk production than that on which Kellner's require- 
ments are based may nevertheless permit very material losses 
of mineral ingredients, especially of calcium, magnesium and 
phosphorus. Complete ash balances are reported for six 
animals on three different rations, all of which maintained the 
live weights of the cows and resulted in gains of body protein. 
With an average live weight of about 935 pounds and an average 
daily milk yield of about 36 pounds (16.38 Kgs.), the calcium 
and phosphorus requirements as computed according to Kell- 
ner's method and the actual amounts supplied in the rations 
were : — 

Table 149. — Calcium and Phosphorus for Milk Production 





Calcium 


Phos- 
phorus 


Estimated according to Kellner 

For production of 36 lb. of milk 


Grams 

31 
44 


Grams 

9 

37 


Total 


75 
43 
16 


46 


Average daily losses from the body 


28 
i-7 



1 Ohio Expt. Sta., Bui. 275 (1916). 



522 NUTRITION OF FARM ANIMALS 

Whether such relatively large losses by fresh cows usually 
accompany copious milk production and are made up again in 
the later stages of lactation, and whether this depletion of the 
mineral reserves of the body is one of the factors in the natural 
shrinkage of milk production, as suggested by Forbes, are 
matters for future investigation. 

It is evident, however, that none of the foregoing data afford 
much information regarding the real ash requirements of dairy 
cows. 

Feed as a stimulus to milk production 

■ 617. Flavoring substances. — By flavoring substances is 
meant those whose presence in small amounts improves the 
odor or taste of a feeding stuff or ration while not adding ma- 
terially to its content of protein or energy. In other words, they 
are substances which do not yield matter or energy to the body 
in the ordinary sense, but which may nevertheless affect the 
course or rapidity of metabolism. 

That the flavor or aroma of feeding stuffs is not an insignif- 
icant element in determining their commercial value, not only 
for milk production but for other purposes, is well established 
by practical experience. This superiority is doubtless due 
largely to the fact that a palatable feed is consumed more freely 
than one lacking in flavor. In the case of milk production, 
however, it appears that, within certain rather narrow limits, 
various flavoring materials may act as a direct stimulus to the 
milk gland, causing a greater yield of milk and especially of fat. 
In Morgen's experiments on milk production cited on previous 
pages extensive use was made of rations consisting largely of 
almost flavorless materials. With such rations it was found 
to be impossible to secure yields equal to those obtained from 
rations supplying equal amounts of protein and energy but 
made up of normal feeds. The addition to these flavorless 
rations, however, of such substances as fennel, anise or hay 
distillate, or the introduction of malt sprouts, caused a distinct 
increase in the milk yield, so that, with rations containing a 
sufficiency of fat, almost or quite normal results were secured. 1 
Moreover, a distinct effect was observed in increasing the fat 
production and the percentage of fat in the milk. 

1 Landw. Vers. Stat., 61 (1904), 1. 



MILK PRODUCTION 523 

Subsequent experiments by Fingerling * fully confirmed these 
results. The addition to the flavorless rations, or to damaged 
hay, of salt, hay distillate, fennel, or even the impregnation of 
rations with the odor of the latter substances, caused a marked 
increase in the yield of milk and in its content of fat as well as 
in the percentage of fat in the milk solids, while similar additions 
to normal rations were without effect. Fingerling's experi- 
ments likewise show clearly, however, that this effect of flavor- 
ing materials, while of much physiological interest, can rarely 
be of much economic importance and they lend no support to 
the claims of the numerous condimental feeds, milk powders, 
etc., so largely advertised. It was also shown that certain 
feeding stuffs (malt sprouts, palmnut cake, cocoa cake and 
beet molasses) when added to a ration of damaged hay and pure 
nutrients increased the milk and fat yields to about the same 
extent as flavoring with fennel. Whether these effects are due 
to some form of nerve stimulus, either general or specific, or to 
an increased production of the hormones of milk production 
(549) does not appear. 

618. Specific effects of feeds. — The fact just noted that 
certain feeds stimulate the production of milk and of milk fat, 
appparently by their influence on the flavor of rations, leads 
naturally to a consideration of the so-called " specific " effects 
of feeds in general. The belief has long been held in practice 
that feeding stuffs may promote milk production and improve 
the quality of the milk to an extent not fully explained by the 
amounts of digestible matter or of energy which they supply. 
On the other hand, there has been no general agreement as to 
what particular feeding stuffs possess this power, and scientific 
investigators have been led to question the existence of such 
effects, particularly upon the composition of milk. A discus- 
sion of the literature of the subject up to 1903 by Lemmermann 
and Linkh 2 affords striking instances of the discrepancies be- 
tween different experiments. The effects of such feeds as 
palmnut meal, cocoa meal, and cottonseed meal, for example, 
are reported by different experimenters as favorable, unfavor- 
able or indifferent. 

^andw. Vers. Stat., 62 (1905), 11; 64 (1906), 357; 67 (1907), 253; 71 (1909), 
373; 74 (1911), 163. 

2 Landw. Jahrb., 33 (1903), 564. 



524 NUTRITION OF FARM ANIMALS 

Defective planning of experiments is doubtless responsible for 
much of this confusion. In many instances the experimenters have 
simply added the feed to be tested to a light basal ration, as in the 
familiar experiments by G. Kiihn * on palmnut meal so frequently 
referred to. Others, while substituting one feeding stuff for another, 
have failed to show that the total amount of digestible matter sup- 
plied was unchanged. In some extensive investigations, for instance, 
oil meals and similar feeds have been interchanged in amounts supply- 
ing equal quantities of protein without regard to other ingredients. 
Under such conditions concordant results could not be expected, and 
one can but agree with Lemmermann and Linkh that the evidence is 
inconclusive, while their own experiments, although indicating specific 
effects for various feeding stuffs, are scarcely more convincing. 

Similar negative evidence is afforded by the extensive feeding 
trials with dairy herds carried out in Denmark by Fjord, Friis 
and S torch and which afford the basis for the so-called " feed 
unit " or Scandinavian system of comparing rations (702). 
In these trials a variety of feeding stuffs, including many re- 
puted to have specific effects on milk production, were compared 
with ordinary farm grains and failed to exert any material 
influence on the milk secretion other than what may be plausibly 
explained by the variations in the protein content and the total 
nutrients of the rations incident to the experimental method. 
In particular, indications of a specific effect on the production 
of milk fat are lacking. 

More positive results have been reached, however, in two 
recent investigations, viz., in a series of investigations by Hansen 
at the Agricultural Academy Bonn-Poppelsdorf and in a series 
of cooperative experiments on palmnut meal made under the 
auspices of the German Agricultural Council. 

619. Hansen's experiments. — Hansen's experiments 2 in- 
cluded nine series on 63 cows, extending over 5 years, in which 
the various feeding stuffs to be tested were substituted in a 
comparison ration for others which appeared to be indifferent 
in this respect. Care was taken to keep the total digestible 
nutrients in the rations, or after the first 3 years, the estimated 
net energy values (starch values), unchanged. 

1 Jour. Landw., 22 (1874), 178. 

2 Landw. Jahrb., 35 (1906), 125 ; 35 Ergzbd. Bd. IV, 327 ; 37 (1908), Ergzbd. Bd. 
Ill, 171 ; 40 (191 1), Ergzbd. Bd. I, 129. 



MILK PRODUCTION 525 

The results show distinct effects of certain feeding stuffs on 
the milk yield which were apparently quite independent of the 
supply of digestible nutrients or of energy values, or of the pro- 
tein supply, and which were consistent when the experiments 
were repeated. 

Hansen 1 distinguishes three groups of these feeding stuffs. 
Those of the first group, including " maizena " (apparently 
gluten feed), maize and oats, increase the quantity of milk but 
depress the percentage of fat, so that the total yield of fat is not 
materially changed. Those of the second group, including 
palmnut meal, cocoa residues, maize distillers' grains, and to a 
less degree linseed and cottonseed meal and the legumes, in- 
crease the total yield of fat without materially affecting the 
quantity of milk, so that the percentage of fat in the milk is 
increased. Those of the third group, including poppy cake, 
" false flax " 2 cake, rice feed and to a less degree sesame cake, 
diminish the yield of fat but do not sensibly affect the quantity 
of milk, so that the percentage of fat is decreased. 

In a subsequent investigation 3 on substantially the same plan, 
Hansen has compared the effects of palmnut cake containing 
respectively 5.55 and 12.42 per cent fat when fed in different 
amounts. He concludes that the specific effect increases with 
the proportion of palmnut cake in the ration and with the per- 
centage of fat contained in the cake. He finds that to secure 
significant results in practice, about 2 pounds per 1000 pounds 
live weight of fat-rich cake and 2 J to 3 pounds of the poorer 
grades are necessary. Different individual animals have dif- 
ferent degrees of susceptibility to the effects of palmnut cake 
but the result can be obtained if sufficient is fed. 

The principal criticism to be made of Hansen's experiments 
is that the experimental periods were so short — usually 7 days 
preliminary and 7 days for the experiment proper. It is not 
an unusual experience in dairy feeding experiments to see a 
change of rations followed by a temporary stimulation of the 
milk production which is not sustained, and the question natu- 
rally arises whether the " specific " effects which seem to be 
demonstrated in the first week or two would have continued 
for a longer time. 

1 Loc. cit., Bd. 40, pp. 187-188. 2 Camelina Sativa. 

3 Landw. Jahrb., 47 (1914), 30- 



526 



NUTRITION OF FARM ANIMALS 



620. Cooperative experiments. — The cooperative experi- 
ments under the auspices of the German Agricultural Council x 
relate to the influence of palmnut cake or meal and were made 
according to a common plan at seven different institutions with, 
in all, 1 86 cows. The experimental periods covered about one 
month each, of which the first 5 to 7 days were regarded as a 
preliminary feeding. The comparison was between 4 pounds 
of palmnut meal per 1000 pounds live weight and an amount 
of a mixture of maize meal and peanut meal supplying equal 
protein and energy values (computed). After correcting for 
the advance of lactation, the substitution of palmnut meal re- 
sulted not only in each of the 7 experiments as a whole, but with 
nearly all the individual cows in a distinct increase of the fat 
production. The total quantity of milk yielded was substan- 
tially unaffected, so that the percentage of fat in the milk was 
increased. The average effects of the palmnut meal were as 
shown in the following table. 

Table 150. — Effects of Palmnut Meal on Milk Production 



Bonn . 

Danzig . . 
Griefswald 

Hamburg . . 

Jena . . . 

Friesdorf . . 
Weihenstephan 



Daily Increase (+) 

or Decrease (— ) in 

Yield 



Milk 

Kgs. 



— O.29 

+ O.58 
+ O.28 
+ 0.09 

— O.04 
+ 0.06 
-f- O.02 



Milk Fat 
Grams 



+ 62 
+ 48 
+ 22 
+ 64 
+ 15 
+ 25 
+ 13 



Percentage of Fat in 
Milk 



On Palm- 
nut Meal 



3-58 
3-25 
3-i7 
3-5i 
3.85 
3-78 
4.21 



On Check 
Ration 



3-24 
2-97 
3-05 
3-17 
3-68 

3-5i 
4-05 



In general, cows that were good milkers seemed more sus- 
ceptible to the effects of the palmnut meal than those yielding 
smaller amounts. It was also observed that the effect did not 
immediately follow the change of feed but developed gradually, 
reaching its maximum in the course of one or two weeks, and 



1 Berichte uber Landwirtschaft, Heft 21 and 23. 



MILK PRODUCTION 



527 



continued for a time after the feeding of palmnut meal was 
discontinued. This fact is of particular interest in its bearing 
upon the interpretation of Hansen's results. 

The evidence of these two series of experiments seems to put 
the possibility of a " specific " effect of certain feeding stuffs 
upon milk production beyond doubt. They open up an inter- 
esting field for further investigation, both as regards the physio- 
logical explanation of the fact and as to its practical significance. 

621. Specific effects associated with fats. — In view of what 
is known regarding the significance of certain fats (or of sub- 
stances associated with them) for growth (498), it is of interest 
to note that these " specific " effects on milk production seem 
to be associated to a considerable extent, although not ex- 
clusively, with the fat consumed. Morgen's investigations 
(613) show that the addition of fat to his flavorless rations had 
such a stimulating effect up to a certain limit. Many of the 
feeding stuffs believed to exert such " specific " effects are 
relatively rich in fat, notably palmnut meal for which the result 
seems best established. Moreover in the case of the latter 
material, as just noted, Hansen finds the influence most marked 
with samples rich in fat. Whether these effects are due to the 
fat as such or to associated substances, as is believed to be the 
case in growth, is a matter for future investigation. 

622. Influence on utilization of energy. — In conclusion, 
it may not be superfluous to point out that the stimulating 
effects of feed on milk production do not necessarily imply any 
higher utilization of the feed energy supplied. Certain feeds 
apparently " speed up " the metabolic processes in the udder, 
but whether the increased production is effected with an in- 
creased or a decreased efficiency cannot be determined from 
experiments of the type thus far made. (Compare Chapter 
XVII, § 1, 737, 738.) 

623. Influence of feed on composition of milk. — The results 
outlined in the last few pages have an obvious bearing on the 
much discussed question of the effect of feeding on the composi- 
tion of milk. That such an influence exists has long been the 
belief of practical dairymen, while the tendency of scientific 
investigation has been on the whole to throw doubt upon it. 
Some writers have gone so far as to practically deny that the 
feeding has any significant influence upon the composition of 



528 NUTRITION OF FARM ANIMALS 

the milk, while others, more conservative, have contented them- 
selves with pointing out the conflicting nature of the evidence. 

624. Influence on percentage of fat in milk. — Since fat is 
the specially valuable ingredient of milk, the discussion has 
centered around this substance. An increase in the percentage 
of fat in the milk may result from an increase in the percentage 
of total solids, i.e., a decrease in the water content, as well as 
from a specific increase in the fat. The conservative view on 
this point was thus summed up by Jordan in 1908. 1 

" This question has been much discussed and much investi- 
gated from the work of Kuhn in 1868 down to the present day. 
Many experiments have been conducted for long periods and 
short periods in which very moderate rations have been com- 
pared with very large ones, highly nitrogenous foods with those 
of a low protein content, dry with green or succulent materials, 
and grains of the same class with one another, and, in a great 
majority of cases, the verdict has been that ' no consistent 
relation appears to exist between the quantity or character of 
the ration and the composition of the milk.' The writer has 
examined the results of nearly all the important experiments 
of this character of which he could find a record, and in but few 
cases could he discover that there was a material increase or 
decrease in the proportion of milk solids which bore a logical 
relation to variations in the ration. In some cases a temporary 
change appeared in the milk immediately after a violent change 
in the ration, but in most instances of this kind there was very 
soon a return to the animal's normal product. In a small 
proportion of experiments, the milk appeared to sustain a per- 
manent though not extensive modification. The weight of 
testimony bears out the statement that the quality of milk 
cannot be changed at will by the farmer, but is largely deter- 
mined by causes not under his control, such as breed and indi- 
viduality, although feeding and treatment, especially the latter, 
have more or less influence upon the character of the milk 
secreted." 

Much of the alleged effect of feeding stuffs upon the com- 
position of milk is associated with the question of the so-called 
" specific " effects of feeding stuffs (618). As was pointed out 

1 The Feeding of Animals, 5th Edition, The Macmillan Co., New York, 1908, 
PP- 3i7-3i8. 



MILK PRODUCTION 5 2 9 

in considering that question, both the planning and execution 
of many of the older experiments were defective and their 
results must be regarded as inconclusive. The more recent 
experiments of Hansen and of the German Agricultural Coun- 
cil, on the other hand, as well as the investigations of Morgen 
Fingerlmg and their associates upon the influence of feed fat 
and of condiments upon milk production, afford numerous ap- 
parently unquestionable instances of an effect of the ration 
upon the fat content of the milk. 

For example, the experiments of the German Agricultural 
Council on palmnut meal (620) showed an average increase in 
the percentage of fat ranging in the different experiments from 
4 per cent to n per cent, while individual cows showed even 
more striking differences. Morgen's results on the specific 
effect of feed fat when added to fat-poor rations (613) and like- 
wise Fingerling's results regarding the influence of condiments 
(617) afford even more striking examples of the same effect 
Apparently it must be admitted that, under some conditions 
the fat content of milk may be distinctly affected by the feeding 
and that this effect appears to be associated with the fat supplv 
of the ration. 

625. Influence on percentage of fat in solids. — Further- 
more it appears from such of these latter experiments as in- 
cluded determinations of the total solids of the milk that the 
increase in fat content was essentially a " one-sided " increase 
i.e., that the proportion of fat to other solids in the milk was in- 
creased. This was notably the case in the majority of experi- 
ments on fat-poor rations, in which the proportion of fat in the 
milk solids was increased by from 12.5 per cent to 23.5 per cent 
by the addition of fat to the feed. Similar although much less 
marked results were also obtained in Fingerling's experiments 
upon the influence of condiments. 

In Hansen's experiments, too, the influence on the fat content 
of the milk was due, in the majority of instances, largely to an 
increase or decrease of the percentage of fat contained in the 
mrik solids, the increase or decrease over the comparison rations 
being over 5 per cent in. fully one-third of the experiments 
while Lmdsey 1 has confirmed Hansen's results as regards 
cocoa meal. 

1 Mass. Expt. Sta., Bui. 155. 
2 M 



530 NUTRITION OF FARM ANIMALS 

It seems clear from the foregoing facts that the proportion of 
fat in the milk solids, as well as the total yield of fat and its per- 
centage in the fresh milk, may be influenced, temporarily at 
least, by the nature of the feed, and it may be presumed that 
some of the results obtained on this point in the earlier and less 
conclusive experiments did, as a matter of fact, represent a real 
effect of this sort. 

626. Significance in practice. — Too much stress must not, 
however, be laid on the physiological facts apparently estab- 
lished by the evidence just considered. It still remains true 
that those major differences in the composition of milk from 
different sources which are of commercial importance are due 
to breed and individual differences in animals (564). As has 
been repeatedly insisted, the prime factor in successful dairy- 
ing is the capacity of the animal as a milk producer. The 
quality of milk best suited to meet the demands of a particular 
market is most easily and certainly secured by intelligent 
breeding and selection, while any influence of the feed is 
essentially a secondary factor. At the same time the results 
seem to indicate that while feed is a secondary factor it is 
not altogether a negligible one. If it is possible by suitable 
selection of feed to permanently increase the fat yield to any 
such extent as has been observed in short experiments, or if, 
on the other hand, it may be depressed by an unsuitable choice 
of feeding stuffs, the matter is one of considerable importance 
and might well be made the subject of large scale cooperative 
investigations similar to those of the German Agricultural 
Council on palmnut meal. 



CHAPTER XIV 
WORK PRODUCTION 

627. Prime purpose of excess feed. — Aside from reproduc- 
tion, the prime purpose for which a mature animal consumes 
feed in excess of its maintenance requirement is the production 
of the external mechanical work required for its diverse ac- 
tivities, either natural in the wild animal or enforced in the 
domesticated work animal. It is true that more feed may be 
consumed than is required for this purpose and that a fattening 
of the animal may result. The latter, however, is simply a 
laying aside of reserve material which may be utilized later 
and, however important economically, may be regarded as 
physiologically incidental. Any considerable fattening of the 
work animal is not only a diversion of energy from the main 
purpose of the feeding but constitutes an extra weight to be 
carried by the animal, while if too extensive it may interfere 
with heart action and respiration. 

Since horses or mules are substantially the working animals 
of the United States, the following discussion will have refer- 
ence chiefly to these animals. 



§ i. The Physiology of Work Production 

Nature of muscular work 

628. The muscles. — Mechanical work is performed by an 
animal by means of its muscles (84, 85), of which there are two 
kinds called, respectively, striped, or striated, and smooth, or 
non-striated, muscles from the appearance of the microscopic 
fibers of which they are composed. The skeletal muscles, by 
means of which external work is performed, are striated muscles. 
They are also called voluntary muscles because they are inner- 

53* 



532 NUTRITION OF FARM ANIMALS 

vated from the cerebrospinal system and are under the con- 
trol of the will. The muscles of the internal organs are chiefly 
non-striated muscles, the heart being the conspicuous exception, 
and are to a very limited degree subject to the will, being in- 
nervated from the sympathetic nervous system. In the study 
of work production, therefore, we have to do chiefly with the 
phenonena of striated voluntary muscles. 

The physiology of the muscle and of muscular contraction 
is a very complex subject and wide differences of opinion exist 
regarding many aspects of it. All that is attempted here is to 
outline such general features as seem necessary for a proper 
comprehension of its relations to nutrition. 

629. Contraction. — When a suitable stimulus, which in 
the living animal is usually a nerve stimulus, is applied to a 
muscle it contracts, that is, it tends to grow shorter and thicker. 
This change is brought about by a shortening and thickening of 
the individual fibers of which the muscle is built up. A single 
stimulus, such, for example, as that caused by the making or 
breaking of an electric circuit, gives rise to what is known as 
a simple muscular contraction or twitch. If such a stimulus is 
repeated with sufficient frequency it produces a series of simple 
contractions which fuse together, resulting in a state of contrac- 
tion which continues, subject to the effects of fatigue, as long 
as the stimulus acts. This form of muscular contraction has 
received the name of " tetanus." In the living animal the 
ordinary contractions of the muscles, brought about by the 
nervous system, even those that seem but momentary, are 
essentially tetanic in their character. 

The term contraction as used in connection with the physi- 
ology of muscle does not, however, necessarily imply an actual 
shortening of the muscle. Contraction may either be isotonic 
or isometric. When the muscle in contracting overcomes a 
constant resistance, as, for example, in raising a weight, the 
contraction is said to be isotonic. When, on the other hand, the 
points of attachment of the' muscle are fixed, evidently no work 
can be done in the mechanical sense but the muscle still con- 
tracts in the physiological sense, i.e., exerts a pull. Such a con- 
traction is called an isometric contraction. 

630. Chemical changes in contraction. — In a muscular con- 
traction, either isotonic or isometric, there occurs a rapid 






WORK PRODUCTION 533 

katabolism of materials contained in the muscle or brought to 
it by the circulation together with a corresponding transfor- 
mation of their chemical energy. This katabolism is in effect 
an oxidation, yielding chiefly carbon dioxid and water, but as 
to the details of the process, the views of physiologists differ. 

Certain general features of muscular katabolism are fairly well 
made out. First the immediate accompaniment of contraction is 
not an oxidation but a rapid, almost explosive, breaking down of a 
substance or substances present in the muscle, causing the produc- 
tion of carbon dioxid. It has been shown, according to Zuntz and 
Loewy, that the muscle contains no free oxygen. Nevertheless, it 
contracts instantaneously when stimulated, while the effects upon 
the blood supply follow later, circulation and respiration being stimu- 
lated by the carbon dioxid and other products formed. Further- 
more, it has been shown that, under certain conditions at least, a 
muscle may continue to contract and give off carbon dioxid in the 
entire absence of oxygen. 

With continued activity of the muscle, there is established more or 
less distinctly a state of equilibrium with the increased blood supply, 
oxygen being taken up by the muscle and carbon dioxid given off, 
while, according to a number of experimenters, the dextrose of the 
blood also disappears during its passage through the muscle. Other 
products of muscular katabolism, notably lactic acid and potas- 
sium mono-phosphate — the so-called fatigue products — tend to 
accumulate in the muscle and diminish and finally suspend its ability 
to respond to a stimulus. Fatigue of the muscles usually results 
from a gradual accumulation of these substances and not from lack 
of material to be katabolized. 

631. Energy transformations. — The katabolism of matter 
which takes place in muscular contraction implies an equiva- 
lent conversion of chemical energy into kinetic energy. The 
energy thus transformed appears finally in the two forms of heat 
and visible motion (work) though the ratio between the two 
may vary widely under different conditions. As regards the 
intermediate stages of this process, relatively little certain 
knowledge is yet available. Broadly, it may be said that 
there are two possible general views. The first of these con- 
siders that the potential energy of the material katabolized is 
first converted into heat, and that subsequently a portion of 
this heat is converted into mechanical motion. The second 



534 NUTRITION OF FARM ANIMALS 

general view considers that heat and work are simultaneously 
produced, a portion of the energy taking one form and a portion 
the other. The former view has been supported by no less 
distinguished an authority than Englemann, but nevertheless 
it has not been generally accepted by physiologists. In par- 
ticular, it is difficult to conceive of the existence in a muscle 
of sufficient temperature differences to account for its observed 
efficiency. In other words, the muscle is not in general re- 
garded as being a heat engine. The prevailing view, stated in 
the broadest outline, is that in the chemical changes conse- 
quent on a stimulus, energy is in part liberated as heat and in 
part expended in producing or maintaining tension of the muscle 
fibers. To use a simple illustration, it is as if by some process 
the elasticity of a cord supporting a weight were to be sud- 
denly increased. The cord would contract and the weight 
would be lifted for a certain distance. In isotonic contraction, 
that is, when the muscles are free to shorten, the increased ten- 
sion set up does mechanical work. In isometric contraction 
this increased tension is also finally converted into heat, as for 
example in the case of muscular contraction applied to simply 
sustaining a weight. In this case no work in the mechanical 
sense is done, but energy is expended in what has sometimes 
been called " static work." A familiar illustration of " static 
work " is the muscular effort required in standing. 

632. Tonus. — In the foregoing paragraphs it has been 
tacitly assumed that before and after a contraction the muscle 
is absolutely relaxed. Such is not normally the case. Even 
in a state of rest, so-called, there is a greater or less degree of 
tension of the muscles, especially during the wakening hours, 
known as tonus or tonic contraction. In other words, the 
living muscle is slightly on the stretch, as is shown by the fact 
that it gapes open when cut or shortens when its connections 
with the bone are severed. This tension, like the much greater 
one set up in active contraction, is maintained, in part at least, 
by a continual katabolism in the muscle, which respires, taking 
up oxygen and giving off carbon dioxid. In other words, the 
" resting " muscle is in a state of slight isometric contraction 
and is doing " static work." According to the principles just 
enunciated, all the energy transformed in such a muscle finally 
takes the form of heat, so that, as indicated in Chapter VII 



WORK PRODUCTION 535 

(348), muscular katabolism is the most important source of 
heat in the animal body. The degree of tonus and conse- 
quently the rate of heat production seems to vary at different 
times and in different bodily conditions. During profound 
sleep it is much reduced. It is probably increased by all con- 
ditions which favor the development of a vigorous muscular 
system. What is ordinarily spoken of as a muscular contrac- 
tion, therefore, and especially a tetanic contraction, is in a sense 
an enormous increase of a condition already existing in the 
muscle. 



Secondary effects of muscular exertion 

The great increase of the muscular katabolism during the 
performance of work gives rise to important secondary effects, 
particularly upon the circulation and respiration. It is a 
familiar fact that in active exercise the heart action is largely 
increased and the breathing becomes deeper and more rapid, 
and that ordinarily the limit to muscular exertion is set, not 
by the power of the muscles themselves but by the ability of 
the heart and lungs to keep pace with the demands upon them. 

633. Circulation. — The circulating blood is the medium by 
which oxygen is conveyed to the muscles and carbon dioxid 
and other products of their katabolism removed. The latter 
function is of special importance because an accumulation in 
the muscle of the products of its own katabolism speedily re- 
duces and ultimately suspends its power to contract. In mus- 
cular exercise, therefore, an increase in the rate of circulation is 
essential to the continued activity of the muscles. For ex- 
ample, in experiments by Chauveau and Kaufmann l the 
ratio between the circulation in the resting as compared with 
the active muscle in the living animal varied between 1 : 3.35 
and 1 : 6.60. Zuntz and Hagemann, 2 in their investigations 
upon the work of the heart, found the average amount of blood 
passing through the heart of a horse per minute to be during 
rest 29.16 liters and during work 53.03 liters. By this increase 
in the rate of circulation through the muscles the carbon di- 
oxid and other injurious products of the muscular katabolism 

1 Comptes rend., 104, 11 26, 1352, 1409. 
2 Landw. Jahrb., 27 (1898), Supp. Ill, 405. 



536 NUTRITION OF FARM ANIMALS 

are rapidly removed and an abundant supply of oxygen is en- 
sured. In fact, it is usually true that during work which is not 
excessive the venous blood contains less carbon dioxid and 
more oxygen than during rest. 

Since the heart is a muscular organ, it is obvious that this 
increase in the circulatory activity must add materially to its 
metabolism. In the performance of work, therefore, there is 
an expenditure of matter and energy, not only for the work of 
the skeletal muscles, but likewise for the additional work of the 
heart. Zuntz and Hagemann in their experiments upon the 
horse just mentioned compute that during moderate work the 
katabolism due to the work of the heart amounts to 3.8 per 
cent of the total katabolism of the body. 

634. Respiration. — The greater activity of the circulation 
consequent upon muscular exertion would be futile were not 
provision made for more efficient aeration of the blood in the 
lungs through an increased activity of the respiration. Under 
the stimulus of the carbon dioxid and other katabolic products 
of muscular activity which enter the blood, the respiratory move- 
ments are increased in frequency or depth or both, as described 
in Chapter IV (194), thus making possible a more rapid gaseous 
exchange between the blood and the air in the lungs. This 
action is usually so efficient that the expired air during work 
contains a smaller proportion of carbon dioxid than it does 
during rest, notwithstanding the fact that the total quantity 
eliminated is much greater. Since respiration, like circu- 
lation, is maintained by muscular action, it is true in the former 
case as in the latter that a greater activity of the function neces- 
sitates a greater metabolism for that purpose. 

Effect of work upon protein katabolism 

As already indicated, knowledge of the details of muscular 
katabolism is still meager. The student of nutrition, however, 
is less directly interested in these details than he is in knowing 
the aggregate effect of the performance of work upon the ex- 
penditure of matter and energy by the body under varying 
conditions, since it is this latter which must be made good by 
the feed supply. Much effort has therefore been devoted to 
studies of the influence of muscular exertion upon the kind and 



WORK PRODUCTION 537 

amount of material broken down in the body during work. It 
will be convenient to consider the effects of muscular work, first 
upon the protein katabolism and second upon the katab'olism 
of non-nitrogenous material. 

635. Early views. — Since the muscles, by means of which 
work is performed, consist largely of protein, it was not un- 
natural for the early physiologists to suppose that the sub- 
stance of the muscle itself was consumed and yielded the energy 
for the work done. This was Liebig's view, although it does 
not seem to have been based upon any actual experimental 
results. He taught that work was performed at the expense 
of a katabolism of protein in the muscles, causing an in 
creased excretion of nitrogenous by-products and an increased 
demand for protein in the feed, while the carbohydrates and 
fats of the feed were regarded as simply heat and fat producing 
materials. 

636. Analogy with engine. — The analogy drawn in Chapter 
VI (274^276) between the body and an engine, however, might 
of itself lead one to question the truth of this view. An engine 
does not do work by burning up its own substance but by burn- 
ing fuel material, and if it is well constructed the wear due to 
the work imposed upon it is comparatively slight. It might 
be reasonably expected, therefore, that the machinery of the 
animal body would prove to be at least as perfectly constructed 
as an artificial machine and at least equally capable of convert- 
ing the energy of fuel material into work without destroying 
the materials entering into its own structure. That such is 
indeed the case under normal conditions was first shown by 
Carl Voit, whose results have been fully confirmed by later 
investigators. 

Voit's first investigation 1 was upon a dog alternately resting 
and doing considerable work on a treadmill both when fasting and 
upon a liberal meat diet. The results are shown in the first of the 
two foUowing tables, while the second contains the average results 
of a later series of similar experiments by Pettenkofer and Voit 2 
on a man. 

A/r ' y^ ersuchun S en uber den Einfluss des Kochsalzes, des Wassers, und der 
Muskelbewegungen auf den Stoffwechsel. i860. Summarized by E. v. Wolff in 
Die Ernahrung der landw. Nutzthiere, pp. 386-388 
2 Ztschr. f. Biol., 2 (1866), 478. 



538 NUTRITION OF FARM ANIMALS 

Table 151. — Effect of Work on Protein Katabolism of a Dog 



Number of Experi- 
ment 



I . 
II 

III 
IV 



Meat 
Eaten 



Grams 
O 



1500 



1500 



fRest 
\Work 

[Rest 
I Work 
[Rest 

fRest 
I Work 
[Rest 
/Work 
\Rest 



Water 
Drunk 



Grams 
258 
872 

123 

527 
125 
182 

657 
140 

412 

03 



Urine 
Excreted 



Grams 

186 

518 

145 
186 

143 
1060 

I330 
1081 

1 164 
1040 



Urea 
Excreted 



Grams 

14.3 
16.6 

II.Q 

12.3 

10.9 

109.8 

117. 2 

109.9 

114.1 
no. 6 



Table 152. — Effect of Work on Protein Katabolism of a Man 



Fasting 

Rest 

Work . 
Average diet 

Rest 

Work . 




Urea Ex- 
creted 



Grams 
26.5 
25.0 

33-6 
36.8 



In the case of the man, while there was a great increase in the 
amount of carbon dioxid and water excreted, there was practically 
no increase in the excretory nitrogen. With the dog fasting or on a 
meat diet only, there was in every case a small increase which Voit 
attributes to a deficiency of non-nitrogenous nutrients and not to the 
direct effect of muscular exertion. 

637. Influence of non-nitrogenous nutrients. — While Voit's 
results seem quite in harmony with present conceptions of the 
animal organism as essentially a converter of energy, they 
aroused considerable criticism at the time and led to an extended 
controversy as to the source of muscular energy. The effect 



WORK PRODUCTION 



539 



of work upon the protein katabolism was repeatedly investi- 
gated under the most varied conditions with results which ap- 
peared upon their face to be conflicting. Some observers found 
a marked increase in the excretion of nitrogen during or following 
work, while in other investigations no such effect was apparent. 
The key to these conflicting results seems to have been first 
discovered by Kellner in 1879 in experiments upon the work 
horse. 1 He found that so long as the total amount of feed was 
ample, variations in the quantity of work performed were 
without effect upon the protein katabolism. If, however, the 
work was increased to an amount sufficient to cause a falling 
off in the weight of the animal, thus indicating that the energy 
supply was insufficient, the excretion of nitrogen in the urine 
increased promptly. Furthermore, it was found that if either 
carbohydrates or fat were added to a ration which was just 
sufficient to enable the animal to perform a given amount of 
work, the demands upon the animal could be correspondingly 
increased without causing any increase in the protein katab- 
olism. This may be illustrated by the following summary of 
an experiment in which the addition to the ration consisted of 
starch and in which the amount of work performed is expressed 
in the number of revolutions of the sweep power dynamometer 
used. 



Table 153. — Effect of Starch on Protein Katabolism of Working 

Horse 







Work, Revo- 


Nitrogen 


Live 




Period 


Dynamometer 


Digested 


In Urine 


Weight 








Grams 


Grams 


Kgs. 


I 1 






300 


121. 1 


107.2 


540.0 


H-a 






600 


121. 1 


I IO. 2 


538.3 


H-b 


► Without starch . . 




600 


121. 1 


II5.6 


533-1 


III 






500 


121. 1 


IO9.4 


532.5 


IV 






,4°o 


121. 1 


IO9.6 


530-7 


I I 

n/ 


With starch . . . 


f8oo 
\6oo 


1 20. 1 
1 20. 1 


H5-5 
109.6 


517. 1 
5I5.4 



1 Landw. Jahrb., 8 (1879), 701 ; 9 (1880), 651. 



540 NUTRITION OF FARM ANIMALS 

The effect of even a small excess of work in increasing the 
nitrogen excretion of the horse was so sharp that Kellner even 
attempted to determine how much work could be performed at 
the expense of a given weight of starch or fat by increasing the 
demand upon the animal up to the point where it just failed to 
cause an increase in the nitrogen excretion and a fall in live 
weight. 

A considerable number of more recent experiments have fully 
confirmed Kellner's conclusion that a deficiency of non-nitrog- 
enous nutrients is the chief cause of the increased protein 
katabolism which sometimes occurs during work and have shown 
that in the presence of a sufficient amount of fats and especially 
of carbohydrates even severe work can be performed without 
increasing the nitrogen excretion. Indeed, moderate work con- 
tinued for a number of days has in some cases been accompanied 
by a gain of nitrogen, a fact apparently quite in accord with the 
common experience that the muscles are strengthened by ex- 
ercise. It is clear that the body normally uses non-nitrogenous 
materials as the source of the energy expended in muscular work, 
exactly as it does in the case of the energy required for its inter- 
nal activities. Only when the supply of non-nitrogenous materi- 
als is inadequate does it resort to the katabolism of protein as a 
source of energy for external work, precisely as it does during 
fasting or on exclusive protein feeding as a source of energy for 
internal work (339, 407). 

Effect of work upon the katabolism of non-nitrogenous matter 

638. Gaseous exchange increased. — In striking contrast 
with the minimal effect of work upon the excretion of nitrogen 
is its very marked effect in increasing the consumption of oxygen 
and the excretion of carbon dioxid and water. This increase 
is too obvious from common experience and too well estab- 
lished scientifically to require more than an illustration. The 
fact of such an increase was shown in the researches of Lavoisier 
and confirmed by the earlier experimenters in this field, such 
as Scharling in 1843, Hirn in 1857 and especially Smith in 1859. 
The investigations of Pettenkofer and Voit in 1866, however, 
appear to have been the first to be executed according to modern 
methods. Their results regarding the influence of work upon 



WORK PRODUCTION 



541 



the protein katabolism have already been cited (636) but may 
be repeated in connection with those obtained with the aid of 
the respiration apparatus. 

Table 154. — Influence of Work on Gaseous Exchange of Man 





Number 
of Ex- 






Water Excreted 






Urea 
Ex- 


Carbon 
Dioxtd 






Oxygen 








Taken 




MENTS 


creted 


Excreted 


In Urine 


Evapo- 
rated 


Up 


Fasting 




Grams 


Grams 


Grams 


Grams 


Grams 


Rest .... 


2 


26.5 


716 


1006 


821 


762 


Work .... 


I 


25.0 


1187 


746 


1777 


1072 


Average diet 














Rest .... 


3 


33-6 


928 


1218 


931 


832 


Work .... 


2 


36.8 


1209 


1155 


1727 


981 



639. Effects are immediate. — Experiment confirms the com- 
mon observation that the increased pulmonary exchange conse- 
quent upon muscular exertion begins almost immediately, 
reaches its maximum in a very short time and disappears 
promptly when the work ceases. This is especially true of the 
absorption of oxygen, of which no considerable amount ap- 
pears to be stored up in the body in the free state. In the case 
of the excretion of carbon dioxid, more or less of this gas can 
be held in solution in the blood and lymph and there is conse- 
quently some slight lag in its excretion. 

In view of this prompt adjustment of the respiration to the 
amount of work, determinations of the pulmonary exchange by 
some one of the forms of respiration apparatus described in 
Chapter VI (297-299) are especially useful in studying the effects 
of work upon the katabolism. The use of this method renders 
it possible to compare the gaseous exchange during periods of 
work with that of the same animal at rest and thus to deter- 
mine very sharply the additional oxygen consumption and 
carbon dioxid excretion caused by a measured amount of 
work. The comparative simplicity of the apparatus required, 
the ease with which the respiratory changes can be followed in 
short periods, and the fact that both oxygen and carbon dioxid 



542 NUTRITION OF FARM ANIMALS 

can be determined, have led to the extensive use of this method 
for investigations upon work production. 

640. Nature of non-nitrogenous material katabolized. — 
Since under normal conditions muscular exertion does not in- 
crease the protein katabolism, it follows that the substances 
oxidized for the performance of work must be substantially 
either carbohydrates or fats. If the former, each volume of 
carbon dioxid given off will correspond to an equal volume of 
oxygen taken up ; that is, the respiratory quotient (296) will 
be i.o. On the other hand, if the material oxidized consists 
solely of fat, the respiratory quotient will be approximately 
0.7, while if both are being consumed, it will have an intermediate 
value. Moreover, it is comparatively simple to calculate from 
the respiratory quotient the proportions in which the two are 
being katabolized. Investigations of this sort show that the 
proportions of fat and carbohydrates katabolized for the per- 
formance of work may vary within wide limits, both groups 
being readily available as sources of energy. 

Sources of energy for muscular work 

641. Proteins vs. non-nitrogenous matter. — Liebig's as- 
sumption (635) of an increase of the protein katabolism in 
muscular contraction implied that the proteins were the source 
of the energy manifested, and this view prevailed for many years. 
When Voit, in i860, showed (636) that muscular exertion is not 
necessarily accompanied by any material increase in the protein 
katabolism, the inference seemed unavoidable that non-nitrog- 
enous materials were the main sources of muscular energy. 
This conclusion, however, was too radical to be at once ac- 
cepted in opposition to Liebig's authority and numerous in- 
genious, but not always convincing, hypotheses were advanced to 
explain the observed phenomena on the assumption that the 
proteins were, nevertheless, the source of the energy expended. 

642. Fick and Wislicenus' experiment. — The first attempt, 
however, at a quantitative comparison of the work performed 
with the energy available from the protein katabolized during 
its performance was the famous experiment of Fick and Wis- 
licenus x in 1866. These observers made an ascent of the Faul- 

1 Vrtljschr. Naturf. Gesell. Zurich, 10, 317. 



WORK PRODUCTION 543 

horn, a Swiss mountain 6418 feet high, after having abstained 
from nitrogenous food for 17 hours, and found that the amount 
of protein katabolized during the six hours occupied by the 
ascent and the seven succeeding hours of rest, as measured by 
the urea excreted, was insufficient, according to their com- 
putations, to account for more than about one- third of the energy 
required to lift their bodies to the height of the mountain, mak- 
ing no allowance for the work of the internal organs nor for 
those muscular exertions which did not contribute directly to 
the work done. They observed no considerable increase in 
the urinary nitrogen over that excreted before the ascent. 

643. Protein insufficient as source of energy. — It is true 
(637) that with an insufficient supply of non-nitrogenous ma- 
terials in the feed muscular exertion may lead to an increase in 
the protein katabolism, but in the many comparisons which have 
been made since the time of Fick and Wislicenus by far more 
refined methods than were available to them, this increase has 
been shown to be entirely inadequate to furnish the energy for 
the work performed. Moreover, even the supposition that the 
energy of the total protein katabolized was all applied to work 
production usually fails to account for the energy expended. 

The facts, then, first, that the chief, and often the only, effect 
of muscular work is to increase the katabolism of non-nitrog- 
enous material; second, that even the total protein katab- 
olism is in most cases insufficient to supply the energy ex- 
pended in work ; and third, that, as Kellner (637) has shown, 
the addition of non-nitrogenous nutrients to the ration enables 
more work to be done ; demonstrate beyond cavil that under 
ordinary conditions of nutrition it is the non-nitrogenous in- 
gredients of the body and of the feed which supply most or all 
of the energy expended in the performance of work. 

644. Functions of proteins. — The foregoing statements 
should not be understood as an assertion that the proteins 
play no part in the production of muscular work. In the first 
place, their katabolism furnishes a considerable amount of non- 
nitrogenous products (229, 233) and that these products are avail- 
able to supply energy for work has been strikingly shown by 
Pniiger. He maintained a dog for about nine months on an 
exclusive diet of almost fat-free meat and showed that on this 
diet the animal was capable of performing large amounts of 



544 NUTRITION OF FARM ANIMALS 

work. Aside from the small quantities of fat and glycogen con- 
tained in the meat the energy for work under these conditions 
could have been derived only from the proteins or their cleavage 
products. These results show clearly that protein may be used 
to a large extent as a source of muscular energy, but it is never- 
theless true that under ordinary conditions, and particularly 
with farm animals, the main supply of energy is, as already 
stated, through the non-nitrogenous ingredients of the feed. 

It is by no means impossible, however, that a certain amount 
of protein katabolism may be necessary in a muscular contrac- 
tion. Such a contraction is a function of the protoplasm of 
the muscle fibers and it is conceivable that a portion of the 
energy arising from the katabolism of the proteins and nucleo- 
proteins of the muscle and ordinarily appearing as heat in the 
resting muscle may be switched off, so to speak, to aid in pro- 
ducing the contraction. In other words, it is possible that a 
certain level of protein metabolism may be necessary in order 
to maintain the most favorable conditions for transforming 
the potential energy of non-nitrogenous materials into work. 1 
Such a fact would, of course, have an important bearing upon 
the amount of protein required for a working animal, but at pres- 
ent the matter belongs in the realm of speculation. 



§ 2. The Efficiency of the Body as a Motor 

General results 

645. Body substance is immediate source of energy. — 

While the energy expended in work production is of course de- 
rived ultimately from the feed consumed, its immediate source, 
as stated in §i (630), is the katabolism of body substance, and 
an animal may perform a considerable amount of labor in the 
fasting state at the expense of stored-up material. It will aid 
in the discussion of the somewhat complicated question of the 
efficiency of the animal as a prime motor to consider first the 
efficiency with which the body utilizes this stored-up energy, 
i.e., to inquire what percentage of the total energy of the body 
material katabolized for work production is recovered in the 

1 Compare Armsby, Principles of Animal Nutrition, pp. 207-209. 



WORK PRODUCTION 545 

work done, deferring to the following section a study of the 
efficiency of the animal as a converter of feed energy into use- 
ful work and of the feed requirements of work animals. 

646. Mechanical efficiency of muscle. — A muscle may be 
regarded as a machine for the conversion of chemical energy 
into mechanical work and one may, therefore, speak« of its 
efficiency in somewhat the same sense as of that of a steam 
engine or an electric motor. By efficiency in this sense is meant 
the proportion of the total energy mobilized during a contrac- 
tion which is recovered in the work done. Thus if an isolated 
muscle lifts a weight of ten grams through one centimeter, it 
does 10 gram centimeters of work, equivalent (308) to 
0.2344 X io -4 gram calories. If the increased katabolism caused 
in the muscle by its contraction were shown to be 0.4688 X io" 4 
gram calories, the efficiency of the muscle would be 
0.2344 -f- 0.4688 = 50 per cent, that is, 50 per cent of the total 
energy mobilized would be recovered as mechanical work. 

Much experimental work has been devoted to the study of 
the single muscle as a machine. The subject is a complicated 
one, and unanimity of views upon it, especially as to the mecha- 
nism of muscular contraction, has by no means been reached. 
As regards the efficiency of the muscle as a converter of energy, 
however, one fact is perfectly well established, viz., that it 
varies within quite wide limits, depending especially upon the 
load as related to the capacity of the muscle and upon the de- 
gree of shortening. 

647. Mechanical efficiency of the body as a whole. — If the 
amount of energy mobilized in each muscle concerned in the 
performance of a certain form of work were known, it is con- 
ceivable that, assuming each muscle to act with its maximum 
efficiency, an average theoretical efficiency might be computed 
for the whole group of muscles. The conditions for the max- 
imum efficiency of a muscle, however, seldom or never obtain 
in the working animal, and consequently this hypothetical 
efficiency is not attained. Of its many muscles, some serve 
largely or wholly to maintain the relative positions of the 
different parts of the body, i.e., their contractions are isometric 
(629) and consequently have an efficiency approaching zero. 
Others contract to a varying extent and under loads less than 
the maximum. Some muscles, owing to their anatomical re- 

2 N 



546 NUTRITION OF FARM ANIMALS 

lations, work at a less mechanical advantage than others, while 
the extent to which a group of muscles is called into action will 
vary with the nature of the work. Moreover, the performance 
of labor by an animal sets up various secondary activities, 
notably of the circulatory and respiratory organs (633, 634), 
which consume their share of energy and yet do not contribute di- 
rectly to the performance of the work, and the extent of these 
secondary activities varies with the nature and the severity of 
the work. Some of these sources of loss of energy are anal- 
ogous to the radiation losses from the cylinder of a heat engine, 
while others are comparable with the internal resistances of the 
engine itself. 

Determinations of the efficiency of the isolated muscle, there- 
fore, afford no adequate means of estimating the efficiency of 
the body as a whole and the latter must be determined by di- 
rect experiment. Such a determination is made by causing 
the animal to perform a measured amount of work under con- 
ditions which also permit the measurement, either directly as 
heat or by the methods of indirect calorimetry described in 
Chapter VI, of the total body energy metabolized. 

Thus in experiments by Benedict and Cathcart 1 upon a man 
riding a bicycle ergometer, the subject breathed through the 
mouthpiece of a Benedict universal respiration apparatus 
(298), by means of which the oxygen consumption and the car- 
bon dioxid elimination could be determined. From these 
data the amount of energy metabolized in the body was com- 
puted and compared with the amount of mechanical work done 
as measured by the ergometer. For example, in one of these 
tests the energy output per minute as computed from the res- 
piratory exchange was 6.32 Cals., while the mechanical work 
done per minute was equivalent to 1.02 Cals. In other words, 
1.02 -7- 6.32 = 1 6. 1 per cent of the total energy output was 
recovered as useful work, the remainder taking the form of 
heat. 

648. Gross and net efficiency. — Comparisons like that of 
the preceding paragraph give what is called the gross efficiency 
of the body, i.e., they show what proportion of the total energy 
metabolized during work is recovered in the useful work done. 
It is analogous to the efficiency of an engine as computed from 

1 Muscular Work; Carnegie Inst, of Washington, Publication No. 187 (1913)- 



WORK PRODUCTION 547 

a comparison of the brake horse power with the steam con- 
sumption. 

But the body katabolizes matter and liberates energy for 
other purposes than the performance of external work, — i.e., it 
has a maintenance requirement for the support of its internal 
work (341, 342) analogous in some respects to the energy re- 
quired to run an engine without load. The subject of Benedict 
and Cathcart's experiment produced during rest (lying on a 
couch) 1.09 Cals. of heat per minute. If this maintenance re- 
quirement be subtracted from the total energy output during 
work there is left 5.23 Cals., as the additional energy output 
required for the performance of the 1.02 Cals. of measured exter- 
nal work. Computed in this way an efficiency of 1.02 -?- 5.23 
= 19.5 per cent results. This has been called the net efficiency. 
It shows the utilization of that portion of the energy output 
which is expended in the physiological processes required for 
the production of external work as distinct from the various 
forms of internal work included in the maintenance requirement. 
In computing the net efficiency in this way difficulty arises in 
deciding upon the proper deduction to be made. Thus in an 
experiment like that just cited, one may subtract from the 
total energy output of the body during work, not only the 
energy expenditure for maintenance during rest but likewise 
that caused by sitting on the ergometer and causing it to rotate 
without load, and the remainder may be regarded as the energy 
metabolized for the performance of the useful work. The 
total output of energy being 6.32 Cals. per minute during the 
work, it was determined that the same subject metabolized 1.13 
Cals. more energy per minute when riding without load than 
when at rest. The added load in the work experiment, there- 
fore, required the expenditure of 6.32 — (1.09 -f- 1.13) = 4.10 
Cals. per minute for the performance of 1.02 Cals. of 
work, from which an efficiency of 24.9 per cent may be com- 
puted. Similarly, in experiments with the work horse one may 
subtract the energy expended during horizontal locomotion in- 
stead of that metabolized during rest and compare the remainder 
with the useful work done. 1 

1 For a discussion of the various base lines for the computation of efficiency, 
compare Benedict and Cathcart's publication already cited, pp. n 2-136, and also 
Reach, Biochem. Ztschr., 14 (1908), 430; Landw. Jahrb., 37 (1908), 1053. 



548 NUTRITION OF FARM ANIMALS 

This method of computation is unlike any usually employed by 
the engineer, and Schreber 1 has criticized it severely. The engineer 
is accustomed to estimate the losses due to the internal resistance of 
an engine by a comparison of brake horse power and indicated horse 
power. No method exists, however, for determining the indicated 
horse power of the animate motor, if indeed it permits of any cor- 
responding conception, and only the method of comparison just out- 
lined is available. It is as if the engineer had no indicator and esti- 
mated the efficiency of his engine by deducting from the total steam 
consumption that required to run the engine empty and compared 
the remainder with the external work done. The internal work of 
the animal, however, like that of the engine, is largely mechanical. 
If, on the basis of Zuntz's computation of the efficiency in locomo- 
tion (662), it may be assumed that this internal work is performed 
with approximately the same efficiency as the external work, then 
the net efficiency of the animal will be somewhat analogous to the 
efficiency of the steam in the cylinder of the engine. 

649. Gross efficiency variable. — It should be observed that 
while the net efficiency may be regarded as substantially con- 
stant under a considerable variety of conditions, the gross effi- 
ciency will vary with' the ratio of work done (load) to main- 
tenance requirements. Thus if Benedict and Cathcart's 
subject had done, only half as much work per minute with the 
same net efficiency, his gross efficiency would have been only 
13.7 per cent instead of 16.1 per cent. 

Total energy expended per minute. 

For mechanical work, 0.51 Cal. -5- 0.195 — 2-62 Cals. 

For maintenance 1.09 Cals. 

Total 3.71 Cals. 

Recovered in work done 0.51 Cals. 

Gross efficiency 13.7 per cent 

Up to the point at which the net efficiency begins to be affected, 
the gross efficiency will increase with increasing load as Bene- 
dict and Cathcart show experimentally to be the case. This 
influence of the maintenance requirement upon the computa- 
tion of the utilization of energy is identical with that to which 
attention has already been called in connection with the utili- 
zation for material products. If the useful work performed 

1 Arch. Physiol. (Pfluger), 159 (1914), 276, 



WORK PRODUCTION 549 

be reduced to zero, as for example in horizontal locomotion, 
the gross efficiency of course also becomes zero. 

650. Efficiency per day. — The figures for either gross or 
net efficiency show the efficiency for the time during which the 
work is being done. Since, however, it is not practicable to stop 
the animal machine when the demand for work ceases, the 
efficiency for the entire 24 hours, i.e., the degree to which the 
body energy is utilized in practice, will evidently vary with 
the number of hours work done per day. Thus if Benedict and 
Cathcart's subject had been able to work 8 hours per day at 
the same rate as in the experiment just cited, his gross efficiency 
for the 24 hours would have been as follows : — 

Energy expended 

480 minutes work ©6.32 Cals. = 3034 Cals. 
960 minutes rest @ 1.09 Cals. = 1046 Cals. 



4080 Cals. 



Work done 

480 minutes @ 1.02 Cals. = 490 Cals. 

Efficiency per day 12.01 per cent 

On the other hand, if he had worked only one hour per day, 
it may be presumed that both the net and gross efficiency of the 
work production during the hour of work would have been 
substantially the same but the efficiency for the 24 hours would 
have been much lower, viz., 

Energy expended 

60 minutes work @ 6.32 Cals. = 379 Cals. 
1380 minutes rest @ 1.09 Cals. = 1504 Cals. 



1883 Cals. 



Work done 

60 minutes work @ 1.02 Cals. = 61 Cals. 
Efficiency per day 3.24 per cent 

In discussions of the efficiency of a man or an animal as a 
motor, and particularly in comparisons with artificial motors, 
it is essential to distinguish clearly whether the net, or the gross 
efficiency is meant and likewise to base the comparisons upon 
the performance per day. Since the net is apparently less 
affected than the gross efficiency by variations in the intensity 
and duration of the work, it appears to be the most logical 



550 NUTRITION OF FARM ANIMALS 

method of comparison in the case of the animal as well as being 
the most convenient in practice. 

651. Analysis of total work. — A quadruped performs work 
by means of locomotion, with or without draft, either horizon- 
tally or on an inclined plane. The work which it performs 
may therefore be subdivided into work of locomotion, work of 
draft and work of ascent and the efficiency for each form com- 
puted separately. The same is of course true of man, but in 
addition other forms of work, such as turning a crank with 
the hands or with the feet (stationary bicycle) or lifting a 
weight directly may be performed. The method of analyzing 
the work of a quadruped has been worked out especially by 
Zuntz and may be conveniently illustrated from Zuntz and 
Hagemann's investigations on the work horse. 1 The methods 
of indirect calorimetry were used, carbon dioxid production 
and oxygen consumption being determined with the Zuntz ap- 
paratus (279) and the corresponding energy output calculated. 
The work was done upon a special tread-power located in the 
open air, and during the rest experiments the animal likewise 
stood in the tread power. The inclination of the platform of 
the power could be varied, and it could also be driven by a steam 
engine, so that by setting it horizontal the work performed by 
the animal was reduced to that of locomotion alone. The dis- 
tance traveled was measured by a revolution counter and in the 
experiments on draft the animal pulled against a dynamometer. 
The apparatus used is illustrated in Chapter VI, Fig. 33 (313). 

652. Horizontal locomotion. — This is an important factor 
in work production, since it requires the expenditure of con- 
siderable energy in successive liftings of the body at each step 
and the overcoming of internal resistances. The energy thus 
expended does not ultimately produce any work in the me- 
chanical sense, but all appears as heat. The work of locomotion, 
therefore, is in a sense not useful work although necessarily in- 
cident to the performance of the work. 

If the tread power be set horizontal and driven by a motor, 
the total energy output by the subject will measure what may 
be called, by analogy with the gross efficiency (648), the gross 
expenditure in locomotion. Subtracting the energy output 
during rest (standing) from the total output during locomotion 
iLandw. Jahrb., 18 (1889), 1; 23 (1894), 125; 27, Ergzbd. Ill, (1898). 



WORK PRODUCTION 551 

shows of course the expenditure in the latter exclusive of that 
required to maintain the body upright (work of standing), 
or what may be called the net expenditure. 

On the average of thirty -five trials upon locomotion at a walk, 
Zuntz and Hagemann found the net expenditure of energy by 
the horse per meter of horizontal locomotion (after correcting 
in the manner described in the next paragraph for the small 
amount of work of ascent due to the fact that the tread power was 
not exactly horizontal) to be as follows per kilogram of weight : 

At a speed of 78 meters per minute . . . 3256 gram calories 
At a speed of 90.16 meters per minute . . . 3666 gram calories 
At a speed of 98.11 meters per minute . . . 3929 gram calories 

The actual amount of mechanical work done in horizontal 
locomotion and converted into heat cannot be measured di- 
rectly. Zuntz and Hagemann, however, have computed it by 
means of a formula proposed by Kellner * and by comparison 
with the figures just given, compute a net efficiency of about 
35 per cent. 

653. Work of ascent. — The animal may also perform work 
by drawing or carrying a load up a hill. Taking the simpler 
case of carrying a load, the total output of energy would be 
expended for three purposes, viz., maintenance (resting value), 
locomotion, and lifting the weight of the load plus body in op- 
position to gravity. Zuntz separates the two latter factors from 
each other by a comparison of two experiments in which the ratio 
of distance traveled to ascent, i.e., the angle of ascent, differs. 

Thus in the thirty-five trials with nearly horizontal locomo- 
tion the average energy output per kilogram of live weight, after 
deducting the maintenance requirement, was 0.4035 gram calo- 
ries per meter traveled. During the same time, however, the body 
was lifted through 0.4395 centimeters, equivalent to 0.004395 
kilogram meters of work of ascent per kilogram of live weight. 
In thirteen experiments on ascending a moderate grade, the 
average energy expended in excess of maintenance per kilogram 
live weight was 1.0795 gram calories per meter traveled, while 
the work of ascent was o. 10 7041 kilogram meters per kilogram. 
Letting x equal the energy per kilogram required for one meter 
of horizontal locomotion and y the energy required for the 

1 Landw. Jahrb., 9 (1880), 658. 



552 NUTRITION OF FARM ANIMALS 

performance of one kilogram meter of work of ascent, the two 
following equations may be formulated : — 

x + 0.004395 y = 0.4035 cals. 
x + 0.107041 y — 1.0795 ca l s - 

From these equations the values of x and y can be computed 
to be as follows : — 

x = 0.3746 cals. y = 6.5856 cals. 

Since one kilogram meter is equivalent to 2.344 cals., it fol- 
lows that the net efficiency in the work of ascent was 
2.344 -1- 6.5856 = 35.73 per cent. In effect, the net efficiency in 
work of ascent is computed by deducting from the total energy 
output the amounts expended for maintenance and for hori- 
zontal locomotion and comparing the remainder with the meas- 
ured work of ascent. The results given in the previous para- 
graph for the energy expended in locomotion were computed 
according to this scheme. 

654. Work of draft. — The net efficiency in draft was com- 
puted by a similar method. The tread power was set nearly 
horizontal. On the average of sixteen trials the total energy out- 
put in excess of maintenance per kilogram live weight and per 
meter traveled was 1.5021 cals., the work of ascent 0.0051 15 
kilogram meters and the work of draft 0.153127 kilogram meters. 
Letting z equal the energy expended in the performance of 1 
kilogram meter of work of draft, the following equation may 
be formulated : — 

x + 0.005115 y + 0.153127 z = 1. 5021 cals. 

Substituting average values for x and y, the value of z is 
7.143 cals., equivalent to a net efficiency of 32.84 per cent. 

655. Correction for speed. — In experiments made at a walk 
it was found that the expenditure of energy per meter increased 
materially as the speed increased, as is illustrated by the aver- 
ages already cited (652) and is shown more fully in a succeed- 
ing paragraph (663). In computing the efficiency of work of 
ascent or draft, it is necessary to take account of this fact. 
The method of doing so is a method of approximation, the de- 
tails of which need not be gone into here. 1 

1 Compare Armsby, Principles of Animal Nutrition, pp. 507-508. 



WORK PRODUCTION 



553 



656. Summary. — The following table contains a summary 
of Zuntz and Hagemann's results regarding the efficiency of 
the body of the horse as a motor. As is apparent from the 
foregoing explanations, the table shows the net efficiency in 
the various forms of work into which the total work done can 
be separated in the manner just described (651, 654). 

Table 155. — Net Efficiency of the Horse in Different Forms of 

Work 



For 1 kgm. work of ascent, without 
load : 

10.7% grade 

18.1% grade . . 

For 1 kgm. work of ascent, with load: 

iS-8% grade 

For 1 kgm. work of draft : 

1.5% grade ' . 

8.5% grade 

Locomotion per kg. mass per meter 

without load: 
Speed of 2.91 miles per hr. . . . 
Speed of 3.36 miles per hr. . . . 
Speed of 3.66 miles per hr. . . . 

The same with load on back : 
Speed of 3.36 miles per hr. . . . 



Work at a Walk 



Net Expendi- 
ture of Energy 



cals. 



6.8508 
6.9787 



6.502 



75190 
10.3360 



0.3256 
0.3666 
0.3929 



0.3914 



Kgm. 



2.9116 
2.9660 

2.7634 

3.1960 
4-393© 



Net 
Effi- 
ciency 



% 



34-3 
33-7 

36.2 

31-3 
22.7 



Work at a Slow Trot 



Net Expenditure 
of Energy 



cals. 



7-3647 1 



7.4240 l 
10.0780 2 



0.5478 » 
0.6007 ' 



Kgm. 



3-1300 



3-iSSo 1 
4.2820 2 



Net 
Effi- 
ciency 



% 



31-96' 



3i-7 ' 
23-4 ! 



657. Relative utilization of fats and carbohydrates. — In 

view of Chauveau's theory 4 that fat must first be converted 
into dextrose, with the elimination as heat of a considerable 
portion of its energy, before it can serve directly as a source of 
energy for the physiological processes, it becomes of much in- 
terest to inquire to what relative extent the energy of fats and 
carbohydrates is utilized in muscular work. 

In Zuntz and Hagemann's extensive investigations, particularly 
in those upon the horse, there were very considerable variations 
in the proportions of fat and carbohydrates katabolized. 'The 
individual trials in which the same kind of work was per- 

1 Single experiment. 2 Two experiments. Work probably excessive. 

3 Independent of speed. 

4 Compare Armsby, Principles of Animal Nutrition, pp. 153-154 and 399-405. 



554 NUTRITION OF FARM ANIMALS 

formed also show in many cases similar variations. Notwith- 
standing this, however, the percentage of energy utilized did 
not vary materially in these instances and there is no indica- 
tion of any such differences as would be expected according to 
Chauveau's theory. 

The question has also been investigated directly by Zuntz 
and his associates in experiments on dogs and on man. In 
these experiments, the feed consisted as largely as possible of 
the nutrient to be tested (protein, carbohydrates or fat, respec- 
tively), so that the body metabolism was largely at its expense. 
The method of investigation was substantially the same as 
that which has just been described. The final results for the 
energy metabolism per kilogram and meter traveled were : — 

Table 156. — Comparison of Nutrients for Work Production 



Proteins only 

Chiefly fat 

Chiefly fat (body freed from carbohydrates by 

phloridzin) 

Much sugar with proteins 

Much sugar and little proteins 



Respiratory 
Quotient 


Energy Metab- 
olism per 
Kilogram and 
Meter 




Gram calories 


0.78 


2.58 


0.74 


2.43 


0.71 


2.71 


0.71 


2.71 


0.88 


2.63 



The differences are quite small, while, as Zuntz points out, if 
2.6 cals. represent the demand for energy per unit of work when 
carbohydrates are the source it should, according to Chauveau's 
theory, rise to about 3.68 cals. when the energy is derived ex- 
clusively from fat. 

Later and more elaborate experiments on man led to the same 
conclusion. Atwater and Benedict, 1 Benedict and Milner, 2 
and Benedict and Cathcart 3 also report experiments upon 
men which, while not regarded as conclusive, indicate a pos- 
sible slight inferiority of fats but one not at all comparable with 
that demanded by Chauveau's theory. On the whole, then, 

1 U. S. Dept. of Agric, Office Expt. Stas., Bui. 136 (1903), 182. 

2 U. S. Dept. of Agric, Office Expt. Stas., Bui. 175 (1907), 234. 

3 Muscular Work ; Carnegie Institution of Washington, Publ. No. 187 (1913), 145- 



WORK PRODUCTION 555 

the conclusion seems warranted that if any difference exists 
in the utilization of the energy of fats and of carbohydrates it 
is too small to be of much practical significance. 

Conditions affecting efficiency 

658. Efficiency varies. — As appears from the foregoing 
summary (656), the net efficiency of the animal body as a 
motor is comparatively high in the case of the horse, considerably 
exceeding in most instances 30 per cent. It may be said in a 
broad general way that with this animal about one-third of the 
energy metabolized for a specific form of muscular exertion (i.e., 
in excess of maintenance or of maintenance plus locomotion) is 
recovered in the mechanical work done. It is also evident, 
however, that the organism has no one fixed degree of efficiency 
but that the latter may vary through a somewhat wide range 
under different conditions. 

659. Forms of work done. — The experiments thus far cited 
refer largely to work done by walking horizontally or up a 
grade, with or without draft. Of all the forms of work yet in- 
vestigated, the ascent of a moderate grade or, in other words, 
the lifting of the body by the legs, appears to be the one which 
is performed most economically, a net efficiency of over 36 
per cent being reported both for the horse and for man. This 
percentage, however, decreases considerably as the angle of 
ascent is increased. For horizontal locomotion, as already noted 
(652), Zuntz computes an efficiency of 35 per cent. Draft up a 
slight grade was performed somewhat less efficiently in the 
case of the horse, the percentage being approximately 31, 
while draft up an 8| per cent grade was done with an efficiency 
of less than 23 per cent. 

Other forms of work appear to be performed with a less 
degree of efficiency. Thus experiments on man in which the 
work was done by turning a crank with the hands have shown 
decidedly lower efficiencies than those in which the work was 
done on a treadmill. The same was true in the experiments of 
Benedict and Cathcart on man, in which the work was done upon 
a stationary bicycle, the maximum figures computed : for the 
net efficiency of 6 subjects ranging from 20.4 to 25.2 per cent. 

1 Loc. cil., p. 125. 



556 NUTRITION OF FARM ANIMALS 

Species. — The difference just noted between the efficiency 
of the human body and that of the horse is evidently due largely 
to differences in the kind of work performed, since the work of 
ascent is done with about equal efficiency in both cases. Klein * 
finds that the work of ascent is performed by the ox with about 
the same net efficiency as by the horse but that the former 
animal expends much more energy in horizontal locomotion per 
unit of distance traveled than does the horse, viz., about 0.53 to 
0.55 gram calories, per meter distance and kilogram live weight. 

660. Individuality. — Zuntz and Hagemann's experiments 
upon the horse show interesting individual differences between 
animals, presumably due to differences in conformation. For 
example, Horse No. XIII carried a given load on his back with 
less expenditure of energy than did Horse No. III. Horse No. 
II expended more energy than Horse No. Ill in horizontal 
locomotion at a walk but less in trotting. No. II likewise 
utilized energy to a slightly less extent than No. Ill in ascend- 
ing a grade and to a considerably less extent in horizontal draft 
but, on the other hand, like No. XIII, carried a load on his 
back more economically than No. III. 

The possible bearing of these facts upon questions of heredity 
and breeding opens up. an interesting field of speculation. 

661. Training and fatigue. — It is a familiar experience that 
any unaccustomed form of work is much more fatiguing at first 
than it is later. This is due in part to the fact that in making 
unfamiliar motions more accessory groups of muscles are called 
into activity than are necessary later when more skill has been 
acquired. The experience of a learner on the bicycle is an ex- 
cellent example of this. In the second place, however, simple 
exercise of a group of muscles in a particular way seems to in- 
crease their average mechanical efficiency. 

This effect may be illustrated by the results of two series 
of experiments by Gruber upon himself in which he de- 
termined the carbon dioxid excreted during work. Thus in 
hill climbing the amounts excreted in twenty minutes were : — 

Series I : 

Hill climbing without practice 40.98 grams 

Hill climbing after 1 2 days' practice .... 32.22 grams 

^entbl. Physiol., 26 (1912), 722. 



WORK PRODUCTION 557 

Series II : 

Hill climbing without practice 38-83 grams 

Hill climbing after 14 days' practice . . . . 31.00 grams 

That the less use of accessory muscles is not the only cause 
of this increase in efficiency is indicated by experiments upon 
convalescents, which have shown that the gradual strengthening 
of the muscles results in a more economical performance of 
their work, largely independent of any special training for a 
particular kind of work. 

Conversely, fatigue has been shown by numerous observers 
to materially increase the relative amount of metabolism per 
unit of work. Schnyder 1 summarizes the matter in the state- 
ment that it is not the work itself but the muscular effort re- 
quired which determines the amount of metabolism, a conclu- 
sion which seems to have anticipated Hill's results 2 regarding 
the relation of muscular tension to metabolism. 

662. Intensity of Work. — It has already been shown (649) 
that the gross efficiency of the body tends to increase with the 
intensity of work, i.e., with the number of units of work per- 
formed in a unit of time, for the reason that the proportion 
of the total energy expended which is devoted to useful work 
increases. On the other hand, common observation tends to 
show that this can be true only within limits, and that excessive 
work is performed uneconomically. 

The intensity of the work may be increased by increasing 
either the speed, the load moved, or the angle of ascent. It 
would be anticipated, therefore, that an undue increase of any 
one of these factors would result in a diminished net efficiency. 

663. Influence of speed. — That great speed in horizontal 
locomotion involves a largely increased expenditure of energy is 
evident. The race horse or the track athlete traveling a mile 
at top speed obviously metabolizes vastly more energy than 
one traveling the same distance at a moderate rate. 

In the case of the horse, Zuntz and Hagemann's results on 
horizontal locomotion at a walk (652) show an increased net 
expenditure of energy per kilogram weight and meter distance 
with increased speed, while locomotion at a trot showed no 
distinct increase up to a speed of about 7^ miles an hour. 

1 Ztschr. Biol., 33 (1896), 289. 2 Jour. Physiol. (London), 42 (191 1), 1. 



558 NUTRITION OF FARM ANIMALS 

Much study has been expended upon horizontal locomotion in 
man. The somewhat extensive literature of the subject as sum- 
marized by Benedict and Murschhauser * shows clearly a marked in- 
crease in the net expenditure of energy per unit of locomotion as the 
speed increases. Brezina and Reichel 2 found that beyond a certain 
maximum speed (about 80 meters per minute) it became an exponen- 
tial function of the velocity, while below that speed only slight varia- 
tions were shown. 

The influence of speed upon the net efficiency in work of ascent 
seems to be much less marked than that upon the expenditure in 
locomotion. No results upon the horse are available. With man, 
Brezina, Kolmer and Reichel 3 in experiments on a tread power found 
that the net expenditure per kilogram and meter distance in walking 
up a grade was substantially independent of speed at velocities con- 
siderably below the maximum just indicated. Since this was found 
to be true also of horizontal locomotion, it follows that the efficiency 
in work of ascent must also have been nearly independent of the speed. 

Benedict and Cathcart 1 found that both the net and gross efficiency 
in work done on their bicycle ergometer, which might be regarded as 
a form of draft, decreased as the speed increased. In none of the 
various experiments cited was there any air resistance, the work being 
done on a stationary apparatus. In actual practice this is an im- 
portant factor at high speeds, increasing very much more rapidly 
than the speed. 

664. Influence of gait. — According to Zuntz and Hage- 
mann's results (656) an increase of speed in the horse obtained 
by a change of gait from a walk to a trot involves a notable 
increase in the net energy expended for locomotion per unit of 
weight and distance, although an increase in the trotting speed 
up to a moderate limit causes no further increase. With man, 
on the contrary, Benedict and Murschhauser find that locomo- 
tion at a given speed is performed more economically in running 
than in walking. 

Such differences are doubtless brought about to a consider- 
able extent by differences in the height to which the body 
is lifted at each step and the degree to which extraneous 
motions, such as swinging the arms in rapid walking, are 
brought into play. 

1 Carnegie Institution of Washington, Publication No. 231 (1915), pp. 12-28. 

2 Biochem. Ztschr., 63 (1914), 170. 

3 Biochem. Ztschr., 65 (1014), 16 and 35. 

4 Carnegie Institution of Washington, Publication No. 187 (1913), 138. 



WORK PRODUCTION 



559 



665. Influence of load. — With the horse, Zuntz and Hage- 
mann find that carrying a load on the back causes a distinct 
increase in the net expenditure for horizontal locomotion per 
unit of mass moved. The work of ascent, on the contrary, 
was performed with at least as high an efficiency by an animal 
carrying a weight as by one without load. With man, Bene- 
dict and Cathcart find the net efficiency but little affected by the 
amount of resistance in their bicycle ergometer. Brezina and 
Reichel find that at moderate speeds the load carried by a man 
affects but slightly the net expenditure per kilogram and meter 
distance but that above the point at which the speed begins 
to affect the latter, the increase is greater as the load is increased. 

666. Influence of grade. — The net efficiency with which 
work of ascent is done decreases as the grade is made steeper. 
Zuntz and Hagemann in their experiments upon the horse ob- 
served a decrease of the efficiency from 34.3 per cent to 33.7 per 
cent as the grade was increased from 10.7 per cent to 18. 1 per 
cent, while for work of draft the efficiency was 31.3 per cent on a 
0.5 per cent grade but only 22.7 per cent on an 8.5 per cent grade. 

That the same is true in the case of man is illustrated in experi- 
ments by Loewy, who obtained the following results on three 
different individuals. 

Table 157. — Influence of Grade on Net Efficiency in Work 

Production 





Net Efficiency 




A. L. 


J. L. 


L. Z. 


23 
30.5 

36.6 


% 

34-3 
34-3 
29.0 


% 

36.1 
32.6 
32.3 


% 
36.6 
36.6 
32.2 



The same conclusion was reached in the recent investigations 
of Brezina and his associates x on man. From an extensive 
series of experiments they compute the net efficiency to have 
been approximately : — 

1 Biochem. Ztschr., 63 (1914), 170; 65 (1914), 16. 



560 NUTRITION OF FARM ANIMALS 

Grade Net Efficiency 

io% 39% 

20% 31% 

30% 27% 

§ 3. Feed Requirements for Work 

As is the case in feeding for other purposes, the working animal 
needs to be supplied with an adequate amount of energy in 
available form and with certain specific forms of matter, par- 
ticularly proteins and ash ingredients. 

The requirements of matter 

667. Functions of protein. — As shown in Chapter IX (418), 
the daily protein requirement of the horse for simple mainte- 
nance is apparently about the same as that of other farm ani- 
mals, viz., approximately, 0.6 pound of digestible crude protein 
per 1000 pounds live weight, although the experimental data 
are rather scanty. 

It appeared in § 1 of this chapter (641-643) that the energy ex- 
pended in muscular work is practically derived from the katab- 
olism of carbohydrates and fats, the protein katabolism being 
unaffected by work so long as an ample supply of non-nitrog- 
enous nutrients is available. One might at first thought be 
inclined to conclude, therefore, that the simple addition of non- 
nitrogenous material to a maintenance ration would suffice to 
enable it to support a corresponding amount of work production 
and that a maintenance ration of digestible protein would also 
be a sufficient supply for the working horse. Such a conclu- 
sion would, however, be premature. It is quite conceivable 
that in order to maintain the muscle as an efficient instrument 
for converting chemical energy into mechanical work, a higher 
plane of protein metabolism may be necessary than is required 
to support it in nitrogen equilibrium when doing no work, 
while the possibility, for example, of a favorable influence of 
an abundant protein supply on the blood circulation and on 
the nervous system should not be overlooked. In fast work 
especially, the demand of the animal for oxygen reaches a 
high level. Since the blood is the vehicle by which oxygen is 
introduced into the body, an adequate stock of blood, or 



WORK PRODUCTION 561 

more particularly of haemoglobin, would be necessary and a 
liberal supply of protein seems to assist in securing this. If 
any of these conjectures should prove to be true the proteins 
may play a not insignificant role in the production of muscular 
work without any evidence of the fact appearing in the total 
nitrogen excretion. 

668. The protein requirement. — No specific investigations 
regarding the minimum protein requirement of the work horse 
seem to have been made, but the extensive experiments of 
Wolff, Grandeau, Muntz and others referred to on previous 
pages afford numerous instances in which entirely satisfactory 
results were obtained from rations comparatively low in pro- 
tein, although in none of them was the supply reduced to the 
maintenance requirement. Similarly, in Langworthy's ex- 
tensive compilation x of rations fed in practice, numerous ex- 
amples of low protein rations are to be found. 

In fact, it would be difficult to compound from ordinary feed- 
stuffs a ration sufficient to support any considerable amount of 
work without introducing more protein than is presumably 
required for simple maintenance. Such being the case, the 
principal point to be taken into consideration is the effect of a 
reduced protein supply upon the digestibility of the ration (723- 
725). Any ration carrying sufficient protein to ensure normal 
digestion would doubtless furnish ample protein for work 
production in all ordinary cases, with the possible exception of 
work at high speed. A nutritive ratio, computed in the usual 
way (709), of 1 : 10 or 1 : 12 would unquestionably ensure ample 
protein for slow work, and probably for moderately rapid work 
also. In the case of man, as is well known, experience or tra- 
dition have led to the general employment of high protein 
rations by athletes. On the other hand, however, Chittenden 2 
has shown that the protein supply of athletes and soldiers, as 
well as that of men of sedentary occupations, may be reduced 
much below the usual level without loss of efficiency. Even in 
these experiments, however, the protein supply was much higher 
than the amounts which recent experiments have shown to suf- 
fice for the maintenance of nitrogen equilibrium in man at rest 
or doing only light work. 

1 U. S. Dept. Agri., Office Expt. Sta., Bui. 125 (1903). 

2 Physiological Economy in Nutrition, 1904. 

2 O 



562 NUTRITION OF FARM ANIMALS 

669. Ash requirements. — As pointed out in previous chap- 
ters, the ash requirements of an animal deserve greater con- 
sideration than they generally receive, while in the case of 
growth, at least, the presence of certain accessory substances 
in the ration is necessary. So far as the working horse is con- 
cerned, however, no sufficient data seem available for a dis- 
cussion of these topics. 



The energy requirement 

670. Economic, or over-all efficiency. — In the preceding 
section certain comparisons were made between the efficiency of 
the animal body as a prime motor and that of artificial engines. 
The animal body, however, is not only a prime motor but in- 
cludes also the furnace in which the fuel is burned and resembles 
in this respect a complete power plant, such as a locomotive, 
for example, rather than an engine. 

Just as the energy of the fuel of a locomotive is subject to 
certain losses due to incomplete combustion and to radiation of 
heat before the steam reaches the cylinders, so portions of the 
energy of the feed escape in the excreta or are expended in the 
various processes incident to the formation in the body of those 
substances whose katabolism yields the energy for a muscular 
contraction. 

Since these losses and expenditures are largely unavoidable, 
they constitute part of the energy requirements of the work 
animal, and from the economic point of view the efficiency of 
the animal is measured by a comparison of the total feed energy 
with the work done. This might be called the economic effi- 
ciency, comparable to the over-all efficiency of a steam plant as 
computed by a comparison of coal consumption with the brake 
horse power obtained. Any such comparisons, of course, 
must take account of the maintenance requirement of the 
animal when doing no work and must therefore be made on the 
basis of the 24-hour output of work (650). 

Few satisfactory direct determinations of the economic effi- 
ciency of work animals in the foregoing sense, i.e., of the re- 
lation of the work done to the feed (or total feed energy) required 
for its performance, have yet been reported. 



WORK PRODUCTION 563 

The extensive investigations on the work horse initiated at Hohen- 
heim by Kellner and continued under Wolff's direction, and which 
have been referred to in Chapter VIII (386 a) in their bearing upon 
the maintenance requirement, were intended primarily to determine 
the energy requirements for work. Unfortunately, however, as there 
noted, the measurements of the work done in the earlier experiments 
were subsequently discovered to be inaccurate. In the comparatively 
few later experiments of 1891-94, various mixed rations were fed. 
While, therefore, the total energy consumed per unit of work could 
be computed, only few and uncertain data for individual feeding 
stuffs can be deduced and the results are therefore of small general 
value for the particular phase of the subject under discussion here. 

671. Net energy values for work production. — The ques- 
tion of the energy requirement of the work animal may, how- 
ever, be approached in a somewhat different way. 

The energy expended in work production, as already stated 
(630, 631), is derived primarily from the katabolism of body sub- 
stances. The function of the feed so far as energy is concerned 
is to replace in the body the energy thus expended. The net 
energy value of a feeding stuff for work production, then, is 
measured by the amount of body energy which it can thus re- 
place. The case is precisely parallel to that of maintenance as 
discussed in Chapter VIII (370). The net energy value of a 
feeding stuff for the latter purpose is measured by the extent to 
which it prevents loss of body energy as a consequence of in- 
ternal work, while the net energy value for the former purpose 
is measured by the extent to which it prevents or makes good 
a loss of body energy due to external work. Conversely, the 
working animal requires in addition to maintenance a supply 
of net energy in its ration equal to the amount of body energy 
katabolized for work production. 

In view of this close similarity between the functions of feed 
in maintenance and in work production, the assumption seems 
warranted that the net energy values of feeding stuffs for these 
two purposes are substantially the same. Thus in an exper- 
iment with a steer already described (364) , it was found that one 
pound of timothy hay contributed 502 Cals. to the maintenance 
of the animal. If the same animal had been required to do 167 
Cals. of external work and had performed it with the same aver- 
age net efficiency as the horse, viz. , about one- third, he would have 



564 NUTRITION OF FARM ANIMALS 

katabolized body substance containing 167 4- § = 502 Cals. 
of energy and it would be anticipated that one pound of timothy 
hay would have been sufficient to replace this energy in the body. 
Similarly, the performance of 1000 Cals. of external work by a 
horse would cause the mobilization of about 3000 Cals. of body 
energy, and the feed necessary to support this work would have 
to supply about 3000 Cals. of net available energy. 

In brief, the net energy values for maintenance, determined 
in the manner described in Chapter XVII and tabulated in the 
Appendix, may be regarded as also net energy values for work 
production, and the energy requirements of the work animal 
may be expressed in terms of these net energy values. 

672. Net energy requirements. — It is plain, in the light of 
the foregoing discussion, that the amount of net energy required 
by an animal for work production may be regarded as equal to 
the body energy metabolized in the performance of the work. 

From the data contained in § 2, it is possible to estimate ap- 
proximately how much energy in excess of its maintenance re- 
quirement must be mobilized in the body of a horse, e.g., to 
perform a known amount of mechanical work of a specific kind. 
Thus a horse in hauling a load having a draft of 100 pounds 
20 miles on a level road would do 10,560 foot tons of mechanical 
work, equivalent to 3421 Calories. Table 155 (651) shows 
the net efficiency of the horse in draft to be about 31.3 per cent. 
Accordingly, the animal would have to mobilize in his body for 
the performance of this work 4321 -5- 0.313 = 10,929 Calories, 
and his feed must therefore supply this amount of net energy 
in addition to the requirements for locomotion, maintenance or 
other purposes. 

The total expenditure of body energy during the performance 
of work by the horse, as appears from § 2, includes substantially 
four factors in varying proportions, viz., the expenditure for 
maintenance, for horizontal locomotion, for ascent (or descent) 
and for draft. A fairly accurate estimate of the net energy 
required to do a certain piece of work may therefore be obtained 
by computing the requirement for each of these factors sepa- 
rately from the data for net efficiency already recorded and 
adding the results. 

For example, let it be supposed that a horse weighing 1100 
pounds hauls a load of 2000 pounds, having a horizontal draft 



WORK PRODUCTION 565 

of 100 pounds, 15 miles per day, including 5 miles up a 1 per 
cent grade, at a speed of 3J miles per hour. The mechanical 
work performed consists of lifting the weight of the animal plus 
the load 264 feet and in overcoming a draft resistance of 100 
pounds through 79,200 feet. The total mechanical work, there- 
fore is as follows : — 

Table 158. — Example of Computation of Work Done 

Draft 100 X 5280 X 15 = 7,920,000 foot pounds = 2.565 Therms 

Ascent 3100 X 264 = 818,400 foot pounds = 0.265 Therms 

Total 8,738,400 foot pounds = 2.830 Therms 

The amount of body energy which the horse must metabolize 
in the performance of this daily task will be that corresponding 
to the mechanical work of draft and of ascent, computed from 
the percentages in Table 155, together with the energy ex- 
pended in locomotion according to the same table and the energy 
requirement for maintenance. The total requirement of net en- 
ergy per day, therefore, will be as follows : 1 — 

Table 159. — Example of Computation of Net Energy Requirement 

For draft 2.565 -f- 0.313 = 8.195 Therms 

For ascent 0.265 -r- 0.343 = 0.773 Therms 

For locomotion 0.262 X 15 = 3.930 Therms 

For maintenance (385) 4.356 Therms 

Total 17.254 Therms 

673. Calculation of rations. — Having in some such way as 
that just illustrated determined the net energy requirement of 
the work horse it is evident that the corresponding ration may 
be computed if the net energy values of the feeding stuffs to be 
used are known. Unfortunately, in the case of the horse, the 
principal work animal of the United States, such net energy values 
of feed stuffs as we now possess have not been directly deter- 
mined but are the results of somewhat complicated calcu- 
lations (775-778) . For the ox, on the contrary, fairly satisfactory 
data regarding the net energy values of feed stuffs are available 
(760, 773, 774), but in this case very few determinations of the 
efficiency of the animal's body in work production have yet been 

J The computation could be somewhat simplified by assuming a uniform net 
efficiency of 5 for all forms of work. 



566 NUTRITION OF FARM ANIMALS 

reported, although the indications are (659) that it is not widely 
different from that of the horse. 

Using the net energy values for the horse obtained by Zuntz and 
Hagemann's method of computation and contained in Table VIII 
of the Appendix, rations may readily be computed for this animal 
in the same general manner as for any other, their accuracy de- 
pending upon the accuracy of the net energy values used. Thus, 
in the case just supposed, the requirement of net energy was 
17.254 Therms. From the figures of the table it is easy to com- 
pute that the following ration would meet the requirement. 

Table 160. — Example of Ration for Work 

Net Energy 

10 lb. meadow hay 3.270 Therms 

10 lb. oats 8.820 Therms 

4.1 lb. maize 5.164 Therms 

17.254 Therms 

The principal difficulty in practice lies in the determination 
of the amount of work done. With farm animals doing a va- 
riety of work at more or less irregular intervals, it seems hardly 
possible to make any computation of the mechanical work 
performed which would be trustworthy or which would justify 
the time consumed. The sufficiency of the ration of the farm 
horse will ordinarily be judged of by the live weight and con- 
dition of the animal, and the principal use of tables of net energy 
values will be as an aid in securing the necessary feed energy 
at the cheapest rate per unit. 

On the other hand, where a large number of horses or mules 
are used for the same kind of work under uniform conditions it 
would seem possible to make fairly reliable estimates of the 
work done and to compute feed requirements with a reasonable 
degree of accuracy. It appears not unlikely that such compu- 
tations might lead to considerable economy, since, as was pointed 
out in considering the maintenance requirements of the horse 
(392), a surplus of feed seems especially apt to stimulate this 
animal to restlessness and an unnecessary expenditure of en- 
ergy in minor muscular activities. 

674. Feeding standards for the horse. — More or less ar- 
bitrary estimates for light, medium, and heavy work may also 
be formulated, as has been done by various writers. 



WORK PRODUCTION 



567 



According to Wiist 1 a horse weighing 1000 pounds is capable 
of performing daily about two million kilogram meters of work, 
inclusive of that of locomotion. Allowing for the work of 
locomotion, this seems to agree well with Thurston's statement : 2 
"It is customarily assumed that a horse may develop 22,500 
foot-pounds per minute throughout a day's work of eight hours." 
If this may be regarded as full work and if the average net 
efficiency of the animal be taken as one-third, the net energy 
requirements for the work itself and the total requirements, 
inclusive of maintenance, would be as follows : — 

Table 161. — Net Energy Requirements of the Horse 



Full work . . 
Half work . . 
One-fourth work 



Work Per- 
formed 



4.688 Therms 
2.344 Therms 
1. 17 2 Therms 



Net Energy 

Required for 

Work 



14.06 Therms 
7.03 Therms 
3.52 Therms 



Total Energy 
Requirements 



18.16 Therms 

1 1. 1 3 Therms 

7.62 Therms 



It should be noted that the discussions of the foregoing pages 
apply specifically to the work horse and the results have only 
a limited application to the feeding of pleasure or race horses. 
With such animals, the cost of feed is economically a very 
minor factor and success depends on experience and skill 
rather than on mathematical computations. That a fairly 
liberal supply of protein in rations for fast work is indicated 
by physiological considerations has been already pointed out 
(667). 

675. Comparison with power plant. — As stated (670), no 
satisfactory direct determinations of the over-all efficiency of 
work animals are recorded, but it may be computed in a case 
like that used as an illustration on a previous page (672, 673). 
There the total useful work was 2.830 Therms, while the gross 
energy of the computed ration would be approximately 55.800 
Therms and the over-all efficiency, therefore, 2.830 -s- 55.800 = 
5.1 per cent. As was shown in § 2 (649) to be the case with the 

1 Cited by Kellner, Die Ernahrung der landw. Nutztiere, 6th Ed., p. 465. 

2 The Animal as a Machine and a Prime Motor, 1894. 



568 NUTRITION OF FARM ANIMALS 

gross efficiency of the body, however, this percentage will vary 
from case to case. It will increase with the intensity of the 
work and decrease with the number of hours the animal is idle 
per day, i.e., it will vary as the ratio of useful work to main- 
tenance requirement varies. In the case supposed, the animal 
worked 6 hours per day. If we imagine his bodily machinery 
stopped for the remaining 18 hours, as an engine might be, and 
charge him with only f of his 24-hour maintenance require- 
ment, the total feed energy necessary would be reduced to about 
45.230 Therms and the over-all efficiency during the hours of 
work, computed on this basis, would be 6.26 per cent, or about 
that of a modern steam locomotive. In actual practice, the con- 
ditions with an animal are very much as if it were necessary to 
keep up a full head of steam for 24 hours or as if an internal com- 
bustion motor were to be run continuously although actual 
work was being done for only a portion of the time. 



■ 



PART IV 
THE FEED SUPPLY 



CHAPTER XV 
THE FEEDING STUFFS 

676. Sources of feeding stuffs. — In the several chapters of 
Part III the feed requirements of different classes of farm 
animals and for different forms of production have been con- 
sidered. 

In the more primitive forms of animal husbandry, such as 
the pastoral husbandry of ancient times or the range feeding 
of the western United States, these requirements were met by 
the consumption of the natural products of the soil. Increas- 
ing population and rising land values, however, inevitably 
tend to the displacement of pastoral agriculture by more in- 
tensive forms in which a much greater variety of feeding stuffs 
is available for domestic animals. Forage crops are grown 
for use in the winter and to supplement the deficiencies of the 
pasture ; grain is produced in excess of the effective demand for 
human consumption and utilized as stock feed ; finally, as this 
surplus of grain decreases with the growing requirement for 
human food, a great variety of residues from the preparation 
of the crude products of the farm for man's use, the by-product 
feeds, becomes available to the stockman. 

It does not fall within the province of the present work to 
consider either the problems of agronomy connected with the 
production of feeding stuffs or the technical details of the 
manufacturing processes which yield the various by-product 
feeds, but a brief consideration of the general properties of the 
principal classes of feeding stuffs seems desirable as an intro- 
duction to the discussion of the principles determining their 
nutritive values 

677. Classification. — The three main classes of feeding stuffs, 
as already stated in Chapter II (111), are the coarse fodders, 
or roughages, consisting of the vegetative organs of plants, the 
roots and tubers, and the concentrates, the latter comprising 
both the grains and similar farm products and the by-products 
of divers industries. The members of these three classes of 

57i 



572 NUTRITION OF FARM ANIMALS 

feeding stuffs may be variously grouped for different purposes, 
but the following scheme, although not strictly consistent, 
may serve the purpose of this discussion. 

Classification of feeding stuffs 

Roughages, or coarse fodders. 
Dried 

Grasses 

Legumes 

Straws 
Fresh 

Grasses 

Legumes 
Silage 
Roots and tubers 
Concentrates 

Farm products 

Cereal grains 

Leguminous grains 

Oil seeds 

Dairy products 
By-products 

By-products of milling 

By-products of fermentation industries 

By-products of oil extraction 

By-products of starch and glucose manufacture 

By-products of sugar manufacture 

By-products of the packing house 

The following characterization of these various classes of 
feeding stuffs is reproduced without material change from an 
earlier article by the writer. 1 



§ i. Roughages, or Coarse Fodders 

678. General characters. — The roughages are charac- 
terized chemically by a relatively large percentage of crude 
fiber, which forms the framework of the plant. They usually 
do not contain very much protein, although in some this ingre- 
dient shows a fairly high percentage. The proportion of crude 
1 Bailey's Cyclopedia of American Agriculture, 1908, Vol. Ill, pp. 58-92. 



THE FEEDING STUFFS 



573 



fat is small and includes much besides true fat. The nitrogen- 
free extract, along with more or less starch and sugar, includes a 
great variety of less familiar carbohydrates and of other sub- 
stances whose nutritive value is problematical. By far the 
larger proportion of the roughages in common use is supplied 
by two classes of plants, — the grasses (Gramineas), including 
maize, and the legumes (Leguminosae) . Furthermore, crops 
belonging to both these classes may be used for fodder when 
but partially mature (hay, maize forage), or they may be al- 
lowed to ripen, the grain may be removed, and the residue 
(straw, stover) used for feeding. 

679. The grasses. — The larger share of the hay crop and 
of the pasturage of the United States is supplied by plants known 
in a restricted and popular sense as grasses, such as timothy, 
blue-grass, red- top. To these must be added, as a most impor- 
tant source of forage in the United States, maize, or Indian 
corn, which botanically is a grass, although not commonly so 
called. The forage supplied by these plants has a very wide 
range of nutritive value, depending on a variety of conditions. 
Chief among these is the stage of maturity at which the crop 
is utilized. In young, growing vegetation the cell walls are 
thin and consist of nearly pure cellulose, while the cells are 
filled with active protoplasm whose chief ingredients are pro- 
teins. Hence, forage cut at this stage shows a relatively low 
percentage of crude fiber and a high percentage of proteins. 
Young and tender pasture grass, relatively rich in protein and 
low in crude fiber, may even approach the concentrates in value, 
as illustrated by the following comparison of the dry matter of 
a sample of young pasture grass with that of average oats : — 

Table 162. — Comparison of Pasture Grass and Oats 





Pasture Grass 


Oats 




Percentage 
composition 


Digestible 
matter 


Percentage 
composition 


Digestible 
matter 


Ash 

Crude protein .... 

Nitrogen-free extract 
Ether extract .... 


9-23 

21.89 
18.25 | 

44-39 J 
6.24 


13.42 

46.06 

3-59 


3-37 

13.26 

( 10.67} 

1 67.08] 

5.62 


IO.39 

54-32 
4.70 



574 



NUTRITION OF FARM ANIMALS 



As the plant matures, the cell walls grow thicker and be- 
come more and more impregnated with tough, woody material. 
At the same time, more soluble carbohydrates, as starch and 
sugar, are being produced, while the protoplasm comes to oc- 
cupy but a small part of the cell. The fully mature forage, 
therefore, is rich in crude fiber of a tough, resistant sort, contains 
much carbohydrate material in general and tends to be poor in 
proteins. For example, three samples of meadow-grass, cut 
at different dates, had the following composition, reduced to a 
uniform percentage of water : — 

Table 163. — Composition of Hay Cut at Different Dates 



June 26 
(over-ripe) 



Water 

Ash 

Crude protein . . , 
Crude fiber ... 
Nitrogen-free extract 
Ether extract . . 



May 14 


June 9 


15.0 


15.0 


7-7 


6.8 


16.1 


9-5 


21.0 


29.6 


37-3 


36.8 


2.9 


2-3 


100. 


100. 



15.0 

6.2 

7.2 
32.4 
36.9 

2-3 
IOO. o 



Accompanying this change in composition goes a decrease in 
digestibility. In the first place, the crude fiber becomes more 
resistant to the action of the digestive organs. Furthermore, 
the less soluble crude fiber seems to have a tendency to pro- 
tect the contents of the cells from digestion. At any rate, 
the percentage digestibility of the protein, and, to a less de- 
gree, that of the other ingredients also suffers. The percentage 
digestibility of the several ingredients of the above samples of 
grass, omitting the ash, was found to be as follows : — 

Table 164. — Percentage Digestibility of Hay Cut at Different 

Dates 



May 14 


June 9 


% 


% 


73-3 


72.1 


79-5 


65-7 


75-7 


61.9 


65-4 


51.6 



June 26 



Crude protein . . 
Crude fiber ... 
Nitrogen-free extract 
Ether extract . . 



% 

55-5 
61. 1 

55-7 
43-3 



THE FEEDING STUFFS 



575 



No determinations of the energy values of these samples were 
made, but it may be fairly assumed that the increasing woodi- 
ness not only diminished the total amounts of digestible nu- 
trients contained but also increased the relative expenditure of 
energy in digestion and assimilation, so that the lesser amount 
of digestible matter in the more mature samples was probably 
less valuable per unit than that of the younger samples. 

When the seeds of grasses begin to form, there is a rather 
rapid transfer of nutritive materials to them from the stalks 
and leaves. The seeds of the ordinary hay grasses, however, 
are so small and so well protected by their seed-coats that they 
either shell out and are lost or largely escape mastication and 
digestion. Grass harvested after the seeds have formed prac- 
tically furnishes straw rather than hay. 

680. Maize. — A somewhat important exception to the 
general rule regarding the influence of maturity is observed 
in the case of maize. While advancing maturity produces its 
normal effects on the stalks and leaves, such large amounts of 
easily digestible material are stored up during ripening in the 
grain, and the latter makes up so large a percentage of the total 
weight of the crop, that it outbalances the effect of increasing 
maturity, and the ripe or nearly ripe crop, taken as a whole — 
i.e., as used for silage or as field-cured forage — is more di- 
gestible than at earlier stages of growth. For example, the 
dry matter of maize forage at three different stages had the 
following composition and digestibility : — 

Table 165. — Composition and Digestibility of Maize Forage at 

Different Stages 





Percentage Composition 


Percentage Digestibility 




Silking 


Kernels 
Glazing 


Nearly 
Mature 


Silking 


Kernels 
Glazing 


Nearly 
Mature 


Ash 

Protein .... 
Non-protein . . . 
Crude fiber . . . 
Nitrogen-free . . 
extract .... 
Ether extract . . 


7-33 
8.99 

4-77 
27.04 

48.28 
3-59 


3-57 

7.08 

1.30 

16.88 

67-15 
4.02 


3-45 

7-65 

0.47 

16.03 

68.69 
3-7i 


58.8 
88.0 
67.7 

71.2 
74-3 


4.9 
46.4 
79.6 
40.0 

76.8 
84.8 


34-8 
63.I 

35-7 
47-2 

81.2 
82.2 


Total dry matter . 


100.00 


100.00 


100.00 


64.2 


66.3 


72.6 



576 



NUTRITION OF FARM ANIMALS 



On the other hand, of course, the digestibility of the stalks and 
leaves alone (stover) diminishes as in the case of other grasses 
as the plant grows older. 

681. Proportions of vegetative organs. — The composition 
and digestibility of the grasses is also materially affected by the 
proportions of the various vegetative organs. The influence of 
the large proportion of seed in the maize plant has already been 
mentioned. In general, the leaves of the grasses, and of other 
forage plants as well, are more tender and contain less crude 
fiber and more proteins than the stems. Leafy species and 
varieties therefore tend to have a higher feeding value than 
those which consist more largely of stems, and any influences, 
such as thickness of planting, manuring, season, and the like, 
affecting the relative proportion of leaves, tend also to affect 
the value of the crop. The combined result of all these factors 
is to make the composition of grass, or of the hay or silage made 
from it, extremely variable. American analyses of timothy 
hay, for example, show total protein ranging from 3.8 per cent 
to 9.8 per cent and fiber varying from 22.2 per cent to 38.5 per 
cent. The corresponding variations in hay from a few other 
grasses are as follows : — 

Table 166. — Protein and Fiber in Various Grasses 



Red-top .... 
Kentucky blue-grass 
Meadow fescue . . 
Orchard-grass . . 
Maize forage x . . 
Oats 



Total 
Protein 



Per Cent 



5.9-10.4 

5-3-12-9 
4.5-11.8 
6.6-10.4 
2.7- 6.9 
5-2- 9-5 



Crude 
Fiber 



Per Cent 

24.0-31.8 
17.7-26.8 
20.8-31.9 
28.9-38.3 
7-5-24-7 
23.1-30.9 



That these variations in composition are accompanied by cor- 
responding differences in digestibility has already been pointed 
out. Moreover, the percentage of crude fiber in roughage 
appears to be a fairly accurate index of the relative expendi- 



Entire plant, usually containing considerably more water than hay. 



THE FEEDING STUFFS 577 

ture of energy in digestion (770). Not only does coarse, woody 
forage contain less digestible matter, but what it does contain 
is less valuable to the animal, pound for pound, than that de- 
rived from forage of a better quality. 

682. The legumes — the clovers, alfalfa, peas, beans, vetches, 
and the like — constitute a source of forage second only to 
the grasses in importance, while their value as renovating 
crops gives them a peculiar position in agriculture. Broadly 
speaking, leguminous forage may be said to differ from that 
of the grasses in two main points. First, under like condi- 
tions it is notably richer in proteins than the latter. Second, 
there is a more marked difference between the physical proper- 
ties of the stems and the leaves in the legumes, the rather coarse 
stems increasing relatively to the leaves with advancing ma- 
turity. Hay from somewhat mature legumes is therefore likely 
to be bulky, to have a higher percentage of crude fiber than 
grass hay, and relatively to be less digestible. For the same 
reason it is more subject to mechanical losses in curing, which 
likewise lower its quality. For all these reasons, the compo- 
sition and digestibility of leguminous forage show an even 
greater range than those of the grasses, and the importance of 
timely cutting is still more marked. In brief, the influences 
which affect the composition and digestibility of the grasses 
affect those of the legumes in substantially the same way but 
to an even greater extent. 

683. Straw consists of the vegetative organs of the plant 
after the removal of the ripe or nearly ripe seeds. Since the 
ripening of the seed consists largely in the transfer to it of sol- 
uble materials from the leaves and stems, it follows that the 
straw will be poor in digestible materials in proportion to the 
extent of seed formation and the degree to which the seeds 
ripen. Furthermore, those parts of the plant most distant from 
the seed are found to be most completely exhausted of food 
material. The straw of the common small grains is relatively 
very poor in proteins and fat, while still containing not incon- 
siderable amounts of digestible carbohydrates and related sub- 
stances. Its tough, woody character, however, as indicated by 
its high percentage of crude fiber, points to a relatively large 
expenditure of energy in its digestion, and its real nutritive 
value is therefore low. Wheat and rye straw stand at the 

2 p 



578 NUTRITION OF FARM ANIMALS 

foot of the list, while oat and barley straw are more val- 
uable. Sheep are especially adapted to utilize straw, consum- 
ing the upper and more valuable parts and rejecting the coarser 
parts. The straw of maize (stover) constitutes a valuable 
feeding stuff. It is relatively less woody than that of the small 
grains, has a relatively high degree of digestibility, and is more 
palatable than ordinary straw. To secure its complete con- 
sumption, however, it is necessary to cut or shred it, and it has 
been questioned whether the additional material eaten in the 
cut fodder is worth the labor of cutting. The straw of the 
legumes is richer in protein than that of the cereals and lower 
in fiber, with correspondingly higher digestibility. On the 
other hand, it is usually coarse and unpalatable, and liable to 
contain molds and other fungi. 

§ 2. Roots, Tubers and Fruits 

684. Contain much water. — Roots and tubers constitute a 
distinct class of feeding stuffs, differing markedly in their prop- 
erties from the coarse fodders on the one hand and the con- 
centrated feeding stuffs on the other. With them may be in- 
cluded for convenience certain fruits, notably pumpkins and 
other cucurbita. They are characterized especially by their 
large proportion of water. In the root crops proper (beets, 
turnips, carrots, mangels and the like) the percentage of water 
may vary from 8o to 95. The tubers (of which potatoes are the 
chief representative) contain less water, the range being ap- 
proximately 66 to 82 per c^nt. A second equally marked char- 
acteristic of these feeding stuffs is the low percentage of crude 
fiber in their dry matter. Their percentage of crude protein is 
also low, and a large share of it consists of non-protein of in- 
ferior nutritive value. 

685. A source of carbohydrates. — The dry matter of these 
crops consists largely of the more readily soluble carbohydrates. 
In the tubers starch is the predominant carbohydrate, while in 
beets, especially sugar beets, cane sugar occupies this position, 
and this substance has been shown to have a distinctly lower 
nutritive value, for ruminants at least, than starch. In other 
root crops, the carbohydrates consist largely of gums, pectin 
substances, and other compounds, including the pentose car- 



THE FEEDING STUFFS 579 

bohydrates, whose exact nutritive value is still uncertain. 
There are also present in roots, and particularly in fruits, 
more or less organic acids whose nutritive value is low. In 
consequence of their succulent and tender nature, tubers, and 
especially roots, have a high degree of digestibility and may be 
presumed to require little energy for their digestion. They 
are therefore a valuable source of carbohydrate material, even 
though some of their ingredients are of somewhat inferior 
value. In general, the dry matter of tubers is more valuable 
than that of roots. On the other hand, the dietetic effects of 
roots are especially prized, but the considerable amount of labor 
required for their cultivation tends to restrict their use. 

§ 3. The Concentrates 

686. Comparison with roughage and with roots. — The con- 
centrated feeding stuffs, or " concentrates," as their name im- 
plies, are those which contain a large amount of nutriment in 
a small weight and bulk. They stand in contrast, on the one 
hand, with roughage, in which the real nutriment is accom- 
panied by a large proportion of woody fiber and other indiges- 
tible matter which adds to the weight and bulk without mate- 
rially increasing the nutritive value. On the other hand, they 
excel the roots and tubers because, while the dry matter of the 
latter is very valuable, it is largely diluted, so to speak, with 
water. The concentrates are therefore the main reliance for 
the rapid, intensive production of meat, milk or work. The 
concentrates may be subdivided into farm products and the 
by-product feeding stuffs. 

Farm products ' * 

687. The cereal grains. — The grains were, until compar- 
atively recent times, the main reliance of users of concentrates, 
and indeed are still in many sections of the United States. 
Corn, oats, barley, rye, peas, beans, rice and at times even 
wheat, are feeding stuffs whose value needs no advocate. These 
seeds contain, stored away for the use of the young plantlet, 
proteins, fats and carbohydrates of the most valuable character 
and " representing the highest type of vegetable food." Their 



580 NUTRITION OF FARM ANIMALS 

nitrogenous matter is chiefly in the form of true proteins of 
recognized nutritive value, their carbohydrates are largely 
starch, and their ether extract chiefly true fat. Being closely 
related to the nutrition of the young plant, the composition of 
the properly matured seed shows much smaller variations than 
that of the coarse fodders. The degree of maturity of the 
seed, however, materially affects its composition and in much 
the same way as it does that of the coarse fodders. ' In the 
early stages of seed formation, the protein and ash flow abun- 
dantly from the vegetative organs to the seed, while later the 
ripening of the seed is largely an accumulation of carbohydrates. 
Any influences, therefore, which check the normal development 
of the seed, such as drought or lodging of the grain, tend to 
produce a seed richer in protein and poorer in carbohydrates. 
Light, shriveled grain, therefore, tends to be high in protein. 
Moreover, the ingredients of unripe seeds differ to a consider- 
able extent from those of ripe seeds. The nitrogen, for ex- 
ample, is to a larger extent in the form of non-protein rather 
than true protein, and the carbohydrates are in the form of sugars 
of one sort or another rather than starch, as in the ripe grain. 
688. Composition and digestibility of cereals. — The cereal 
grains are characterized by a medium percentage of protein 
(8 to 14 per cent), chiefly composed of true protein, a rather 
low percentage of fat (1.5 to 6 per cent) and a high percentage 
of carbohydrates, largely starch. Their ash is small in amount 
and in it potassium and phosphorus acid are prominent, while 
but little calcium is found. Maize contains rather less protein 
than the other cereal grains, with correspondingly high percent- 
ages of starch and of fat. While it has been shown that the 
protein content of corn can be notably increased by selection and 
breeding, the effects of the latter have not yet sensibly affected 
the character of the commercial crop. The naked grains (maize, 
rye, wheat) show a comparatively high percentage digestibility, 
and both in this respect and as regards their composition ex- 
hibit less variation than the hulled grains (oats, barley). In 
the latter, the variable proportion of the relatively valueless 
hulls to the kernel causes both composition and digestibility to 
vary greatly. Oats, for example, have shown the extremes of 
6 and 17 per cent protein and 3 to 7 per cent of fat. The hulls 
resemble straw in composition and value. They therefore in- 



THE FEEDING STUFFS 581 

crease the proportion of crude fiber in the grain, and corre- 
spondingly diminish its digestibility and nutritive value. 

689. Uses of cereals. — The place of the cereal grains in feed- 
ing practice is clearly indicated by the foregoing statements. 
They enable the feeder to introduce into his rations, without 
unduly increasing their bulk or weight, large amounts of easily 
digestible and highly nutritious ingredients. Of themselves, 
they contain a fair proportion of protein for many purposes, 
especially for mature animals, but they are not capable of 
offsetting a deficiency of protein in the other ingredients of 
the ration, nor do they supply enough of this ingredient to meet 
fully the demands of the rapidly growing animal or the highly 
productive dairy cow. 

690. Leguminous grains. — The leguminous grains share the 
general physical properties of the naked cereal grains, and like 
them contain feed materials (proteins, carbohydrates, fats) of 
the highest grade. They are especially characterized, in con- 
trast with the cereal grains, by their relatively high percentage 
of protein, ranging according to American analyses from 20 
to 42 per cent. Some of them, as the soybean and the lupine, 
also carry notable amounts of fat, but the more common ones 
are not richer in this substance than the cereals. They are 
richer in ash than the cereals, notably as regards phosphoric 
acid and lime. Their digestibility is generally high. Like the 
cereals, they are valuable as sources of total digestible feed in 
a concentrated form, but unlike these they serve also to enrich 
rations in protein. Aside from certain technical by-products, 
they are the most available materials for this purpose, and the 
culture of leguminous feeding crops, both for this purpose and 
for their effects on the soil, deserves careful consideration. 

691. Oil seeds. — The oil seeds, such as flax, cotton and 
rape, are not commonly used directly as feeding stuffs because 
of their commercial value. These seeds contain a high per- 
centage of protein, while in place of much of the carbohydrates 
of the cereals and legumes a large percentage of oil is found. 
Flaxseed contains a considerable quantity of so-called " mu- 
cilage," which swells up with water to a slimy mass and has a 
very soothing effect on the digestive organs. Cottonseed is 
fed to cattle to some extent, usually either boiled or roasted, but 
is regarded as dangerous for growing swine. 



582 



NUTRITION OF FARM ANIMALS 



By-products 

692. Nature. — The by-product feeding stuffs are the resi- 
dues of technical processes by which the products of the soil 
are prepared for man's use, either as food or for other purposes. 
The more important of these technical processes are : the mill- 
ing of grains ; the manufacture of cereal foods ; the manufac- 
ture of alcoholic liquors ; the manufacture of starch and glu- 
cose ; the manufacture of sugar ; and the extraction of oils. 

693. By-products of milling. — Milling residues, particularly 
of wheat, are among the most familiar of the by-product feed- 
ing stuffs. They include the screenings secured in cleaning the 
grain for milling and the bran and middlings secured in the 
grinding proper. The screenings are an exceedingly variable 
mixture according to the quality of the grain, containing, be- 
sides light and broken grains, a great variety of weed seeds, 
fragments of straw, sand and earth, as well as spores of numer- 
ous fungi, and dirt of all sorts. While some of these have un- 
doubted feeding value, the possible danger to the health of the 
animals, and of the infestation of the fields with weed seed 
through the manure, demand great caution in the use of 

screenings as feed. Its ad- 
dition to bran or middlings 
is to be regarded as an 
adulteration. 

Bran . — The bran of wheat 
or rye consists essentially of 
the seed-coats of the grain, 
the layer of so-called gluten 
cells immediately beneath 
them, and a proportion of 
the inner, floury part of the 
grain varying with the per- 
fection of the milling. The 
seed-coats of the grain con- 
tain most of its crude fiber, 
while the gluten cells are 
richer in proteins than the inner part of the kernel. In pro- 
portion, therefore, as the bran is more perfectly separated from 
the flour, does it become at once richer in protein and in crude 




Fig. 43. — Partial section of wheat grain. 
(Bailey's Cyclopedia of American Agricul- 
ture.) 

i, Seed pod. 2, Outer seed coat. 3, Inner seed 
coat. 4, Gluten cells. 5, Starch cells. (Jordan.) 



THE FEEDING STUFFS 583 

fiber and poorer in easily digestible carbohydrates. Such bran 
is more valuable as a source of protein than the more floury 
bran, but at the same time contains less total digestible mat- 
ter, and probably has an inferior value as a source of energy. 

Middlings, as the name indicates, are intermediate products 
between bran and flour. In modern , methods of milling, va- 
rious grades are produced, in the names of which there is a 
considerable lack of uniformity. The " brown " middlings 
contain more of the seed-coats (bran) than the " white " mid- 
dlings, which approach the low-grade flour (" red dog " flour) 
in character. Shorts seem to be substantially the same as 
middlings. Because of their smaller content of hulls, mid- 
dlings are decidedly more digestible than bran, while scarcely 
inferior to it in percentage of protein. 

Buckwheat middlings, a by-product from the milling of buck- 
wheat, contains nearly twice as much protein and fat as aver- 
age wheat middlings, and correspondingly less carbohydrates. 
It is sometimes called buckwheat bran, but this name is also 
applied to the tough, innutritious hulls of the buckwheat, which 
have little feeding-value and which are not infrequently used 
as an adulterant of the middlings. The middlings are credited 
with a tendency to ferment or become rancid when stored in 
bulk, and also with producing a soft, oily butter-fat when fed 
in large amounts. 

Rice bran resembles wheat bran, but contains less protein 
and fully twice as much fat. The pure bran is sold largely 
under the name of rice meal, while the commercial bran con- 
tains an admixture of varying amounts of rice hulls. The 
hulls, which are separated from the kernel as the first process 
in the milling, contain about 40 per cent of fiber, and are heavily 
impregnated with silica and covered with hard, silicified fibers 
which are liable to cause severe and even fatal irritation of the 
digestive organs. Their presence in the bran to any large 
extent is to be regarded as a dangerous adulteration. 

Rice polish results from the polishing of the rice grains after the 
removal of the bran and germ. It contains somewhat less fat and 
protein than the pure bran, but is considerably more digestible. 

All these rice by-products contain more or less grits or 
fragments of the kernel, which have been found to be rather 
difficult of digestion. The rice products are also rich in fat, 



584 



NUTRITION OF FARM ANIMALS 



which becomes rancid rather easily and often renders the ma- 
terial unpalatable. It is asserted that this rancidity can be 
prevented by kiln-drying the bran or polish as soon as produced. 
Uses of milling by-products. — There has been a tendency 
to regard the milling by-products largely as sources of protein. 
While it is true that the bran and middlings are richer in pro- 
tein than whole wheat or other cereal grains, the difference is 
not sufficient to enable them to offset to any marked degree 
the deficiencies of other ingredients of the ration in this respect. 
They are to be regarded primarily as sources of digestible 
matter as a whole, with a tendency to increase somewhat the 
proportion of protein in the ration. Familiarity with the good 
qualities of wheat bran in particular, its comparative safety as 
a feed in inexperienced hands, and its good dietetic effect have 
tended to an exaggerated idea of its feed value. When it rules 
high in price it is usually possible to substitute other feeding 
stuffs for it, partially or wholly, which will furnish both pro- 
tein and energy more cheaply. Buckwheat middlings, on the 

contrary, often furnish a 
cheap source of protein for 
a ration otherwise deficient 
in it. 

694. Breakfast food resi- 
dues. — In the manufac- 
ture of the great variety of 
so-called cereals, or break- 
fast foods, now on the mar- 
ket, a considerable quantity 
of by-products accumu- 
lates. In the case of the 
most common of these, 
oatmeal, the residue con- 
sists chiefly of the hulls of 
the oats together with some 
of the lighter grains. 
Oat hulls. — The hulls 
Fig. 44- — Partial section of oat grain, themselves^ have scarcely 

(Bailey's Cyclopedia of American Agricul- more feeding value than 

ture "- ) the straw, which they 

o, Hull, i, Seed coat. 4, Gluten cells. 5. Starch 11 • • ,• 

cells. (Jordan.) resemble in composition, 




THE FEEDING STUFFS 585 

while the proportion of light oats is not sufficient mate- 
rially to raise the value. Oat hulls are rarely offered as such 
in the market but are usually disposed of in one of two 
ways. First, they are made the basis of various proprietary 
feeds, cheap by-products of various sorts being added, usually 
including a small amount of the protein-rich by-products shortly 
to be described. These feeds are offered under various names 
and with abundant advertising testimonials. While they are 
by no means worthless, it is evident that the oat hulls themselves 
are no more valuable because of the addition to them of other 
materials, while the consumer ultimately pays the cost of mix- 
ing, transportation and advertising. The second use to which 
oat-hulls are put is the adulteration of the mixed feeds, es- 
pecially corn and oat feeds, which are freely offered on the 
market. Since it is difficult to recognize even a considerable 
adulteration of this sort, such mixed feeds should be purchased 
only from manufacturers of known integrity or under a satis- 
factory guarantee as to purity. 

Barley feed, a by-product of the manufacture of pearled 
barley, is similar in feeding value to oat hulls. 

Hominy feed. — In the manufacture of hominy from corn, 
the hull, the germ and the more starchy parts of the kernel are 
rejected and constitute hominy feed, or hominy chop, which 
is similar to the whole kernel in composition and digestibility, 
except that its percentage of fat is greater. Consequently it 
has a somewhat higher feeding value, although the fat is likely 
to become rancid on long keeping and thus lower its quality. 

695. By-products of the fermentation industries. — The 
manufacture of alcoholic liquors consists essentially in the 
conversion of the starch of grains or potatoes into sugar and 
the subsequent fermentation of this sugar by means of yeast. 
The resulting liquor may be consumed directly (beer, ale) or 
it may be distilled, yielding the more concentrated distilled 
liquors or commercial alcohol. 

Malt sprouts. — The first step in the process is the prepa- 
ration of malt, by allowing moistened barley to germinate. 
The growth of the sprouts is stopped by drying when they 
are about one-third inch long, and these dried sprouts, sepa- 
rated from the grain, constitute malt sprouts. Being young 
roots of barley, they have the general properties of all young 



586 NUTRITION OF FARM ANIMALS 

plant growth, containing a high percentage of nitrogen, much of 
it in the form of non-protein, and a low percentage of crude fiber. 

Brewers 7 grains. — The next step in the process is the mash- 
ing of the ground malt and other grain with warm water. In 
this process, the diastase of the sprouted barley acts on the 
starch of the grain, transforming it into sugar. In the manu- 
facture of beer or ale, the resulting liquid is drawn off and fer- 
mented separately, leaving a residue known as brewers' grains, 
which is used extensively as a dairy feed. In the fresh state it 
is valuable, but is subject to the disadvantage of fermenting or 
souring very readily, and tending in this state to injure the 
quality of the milk. Somewhat recently, economical pro- 
cesses for drying it have been perfected, and the dried brewers' 
grains constitute a valuable feed which can be shipped like 
any other dried feed. 

Distillers 7 grains. — In the preparation of distilled liquor or 
alcohol, the liquid is fermented in contact with the grains and 
the alcohol then distilled off, leaving a residue known as dis- 
tillers' grains or distillery slop. This residue is much wetter 
than brewers' grains, but is less subject to fermentation, since 
the sugar has been more completely removed. Large quantities 
of it are now put on the market in the dried form, both under 
its own name and various trade names, some of which contain 
no suggestion of the real nature of the material. It constitutes 
a valuable source of stock feed. The grains produced from rye 
are regarded as the poorest and those from maize as of the best 
quality. 

In all these processes the object is to convert the starch of 
the grain as completely as possible into sugar and then into 
alcohol. This results in increasing the percentage of all the other 
ingredients in the residues. They contain accordingly a high 
percentage of protein with also a somewhat greater percentage 
of crude fiber than the ordinary grains. They serve, therefore, 
not only to supply digestible matter as a whole but also to 
correct a deficiency of protein in the ration. 

696. By-products of oil extraction. — The extraction of com- 
mercial oils from various oil-bearing seeds leaves by-products, 
called oil cake or oil meal, some of which have a high feeding 
value. Of these, cottonseed and linseed meal are the only ones 
extensively used in the United States and are typical of the 



THE FEEDING STUFFS 587 

others. The seeds of cotton and flax are rich in both fat and 
protein. Hulled cottonseed contains about 30 per cent of each 
and flaxseed about 22 per cent protein and 35 per cent fat, the 
latter percentage, however, being somewhat variable. The oil 
is extracted from the seeds either by pressure or by the use of 
solvents, leaving a residue still containing some fat and very 
rich in protein. 

Cottonseed meal. — At present cotton oil is extracted only by 
pressure, the resulting hard cake being ground to cottonseed 
meal. The highest grade of cottonseed meal is made from the 
hulled seed and contains 40 to 44 per cent of crude protein and 
8 to 9 per cent of fat. It should be nearly free from the hulls 
and therefore contain little crude fiber. Cottonseed meal is 
adulterated extensively with the tough, black hulls of the 
cottonseed, which have a very low feeding value. This is es- 
pecially true of the inferior grades of commercial cottonseed 
meal, which are sold at a lower price than the standard grade. 

Linseed meal. — Linseed oil is extracted from the flaxseed both 
by pressure and by means of naphtha, the latter being com- 
pletely removed from the resulting oil-meal and recovered for 
use again. The " new process " of extraction removes the fat 
more completely than the " old process " of pressure, and the 
resulting linseed meal is somewhat poorer in fat and contains 
somewhat more protein than the old-process meal. The pro- 
cess of extraction by pressure has been so far perfected in recent 
years, however, that the difference between the old-process and 
new-process meal is distinctly less than formerly. The protein 
of the new-process meal appears to be slightly less digestible 
than that of the old-process meal, which tends still further to 
reduce the difference between the two. 

Other oil meals. — Oils are also manufactured commercially 
from the seeds of the common peanut, the soybean, the oil 
palm and the cocoa palm. The resulting oil cakes or meals are 
extensively used as feeding stuffs in European countries but do 
not appear to have as yet found access to the feed market of 
the United States to any considerable extent. 

The corn-germ meal mentioned in connection with the gluten 
feeds may also be classed as an oil-meal. 

697. By-products of starch and glucose manufacture. — 
Starch and glucose are made in the United States chiefly from 



5 88 



NUTRITION OF FARM ANIMALS 




maize. The starch is separated by coarse grinding and the 
use of water, the starch being carried off in suspension and al- 
lowed to settle out. Glucose is manufactured by further treat- 
ment of the starch with acid. In the preparation of the starch, 
the parts of the kernel which are rejected are the hull, the germ 

and the more glutinous part 
of the interior of the grain 
from which the starch cannot 
be completely separated. 

Corn {maize) bran. — The 
hulls are comparatively low 
in protein and contain con- 
siderable fiber. When sold 
separately they are called 
com bran, although the com- 
position of commercial sam- 
ples indicates some admix- 
ture of the germs. 

Germ meal. — The germ 
contains about 30 per cent 
of oil, which has a com- 
mercial value and is secured 
by pressing the germs. The 
residue constitutes germ meal, which still contains about 7 
per cent of oil, and in the neighborhood of 1 1 per cent of crude 
protein. 

Gluten meal and feed. — The glutinous residue of the kernel 
constitutes gluten meal, containing, in general, 30 to 40 per 
cent of crude protein with a comparatively low percentage of 
fat and fiber. Some factories mix the gluten meal and the hulls, 
and sell the mixture under the name of gluten feed, which con- 
tains approximately 24 per cent of crude protein, 6 per cent of 
crude fiber and 6 per cent of fat. Sometimes the hulls and 
germs are sold together under the names " sugar feed " or " starch 
feed," either wet or dry. In fact, various mixtures of the three 
main products are made and sold under diverse commercial 
names. These various glucose products should invariably 
be purchased on a guarantee as regards composition and purity. 
698. By-products of sugar manufacture. — Sugar has come to 
be manufactured from sugar-beets to a considerable extent in 



Fig. 45. — Partial section of maize kernel. 
(Bailey's Cyclopedia of American Agricul- 
ture.) 

1, Outer layer of skin. 2, Inner layer of skin. 
4, Gluten cell. 5. Starch cells. (Jordan.) 



THE FEEDING STUFFS 589 

the United States, while in certain regions the manufacture 
from sugar cane is an important industry. 

Sugar-beet pulp. — The sugar is extracted from the finely 
cut beets by means of water in what is known as the diffusion 
process. The residue from this constitutes what is commonly 
known as beet pulp, which is essentially sugar beets minus the 
sugar and some of the other soluble substances. In the fresh 
state it contains 90 to 95 per cent of water, which may be re- 
duced to about 85 to 87 per cent by pressing. Its general 
properties are similar to those of roots and it occupies much the 
same place in the ration. Its digestible matter consists chiefly 
of carbohydrates belonging to the group of pectins and gums, 
somewhat inferior to the sugar of the beets but, according to 
recent investigation, fully as valuable as the digestible matter 
of mangels. The wet beet pulp is too heavy to bear long trans- 
portation, but may be preserved in the neighborhood of the 
factory by ensiling. It is now, however, dried and put on the 
market as dried beet pulp, containing not more than 5 to 10 
per cent of water. The dried pulp is relatively about equally 
valuable with the wet pulp, especially if soaked in water, as it 
should be before feeding. 

Molasses. — In the further manufacture of sugar either from 
sugar beets or sugar cane, there remains, as a final residue, the 
molasses. This contains 20 to 25 per cent of water, approxi- 
mately 50 per cent of sugar, scarcely more than one-half per 
cent of true protein, and 8 to 10 per cent of non-protein, along 
with other substances of doubtful nutritive value. It is essen- 
tially a source of easily soluble carbohydrates, principally 
sugar. Beet molasses, in particular, has a marked laxative 
action, commonly ascribed to the potassium salts present in it 
but perhaps due quite as much to the sugar. For this reason, 
care is required to accustom animals to it gradually and not to 
overfeed with it. Its laxative qualities are said to be valuable 
when used in small amounts for horses in preventing attacks of 
colic. 

Molasses feeds. — Owing to its physical properties, molasses 
is an inconvenient material to handle. To avoid this difficulty, 
the so-called molasses feeds have been put on the market. 
These consist of molasses dried down on some suitable material. 
A large number of concentrated feeding stuffs have been used 



590 NUTRITION OF FARM ANIMALS 

for this purpose, and it has also been dried together with the 
beet pulp, forming molasses pulp. All these feeds are of value 
in proportion to the materials out of which they are made. 

699. By-products of the packing house. — The slaughtering 
of meat animals on a large scale in the modern packing house 
yields a number of highly nitrogenous by-products which are of 
especial value in the feeding of swine and poultry. 

Dried blood is especially rich in protein, of which it contains 
over 80 %, practically all of which is digestible. It contains a 
small amount of fat and but little ash. 

Tankage consists essentially of the residue left after the 
rendering of the meat scraps, trimmings and scrap bones of 
the packing house. Tankage contains much less protein than 
dried blood but, on the other hand, contains a considerable per- 
centage of fat, while the bone which it contains renders it rela- 
tively rich in ash ingredients, especially calcium and phos- 
phorus. As is obvious from the method of its manufacture, 
tankage is likely to vary widely in composition and should 
always be bought on a guarantee. 



CHAPTER XVI 

RELATIVE VALUES OF FEEDING STUFFS 

As soon as live stock husbandry emerged from the pastoral 
stage and man began to store up forage for the winter or to 
utilize the products of his cultivated land for feeding his do- 
mestic animals, the question of the relative values of the dif- 
ferent feeding stuffs necessarily arose. As agriculure has 
gradually become more intensive and as the variety of natural 
materials and of technical by-products available has increased, 
the question has grown in importance, the traditions of prac- 
tice based on the experience of earlier investigations have been 
recognized to be insufficient guides, and much effort has been 
put forth to replace these traditions by exact knowledge. 

§ i. Direct Comparisons of Feeding Stuffs 

700. Hay values. — A natural and logical method of inves- 
tigation was to feed the materials in question to animals and 
compare the amount of increase or of milk which was secured. 
Good meadow hay was universally regarded as a complete feed, 
suitable for practically all purposes. Hence it was naturally 
taken as the standard and the effort was made to establish from 
the results of experience and experiment what amounts of dif- 
ferent feedstuffs would replace a unit weight of hay. In this 
way arose the tables of so-called hay values. 1 The first of these 
was that published by Thaer in Germany in 1809, based chiefly 
on the early chemical analyses of Einhof in which the con- 
stituents soluble in water, alcohol, dilute acids and dilute alka- 
lies were determined. The sum of all these ingredients, with- 
out distinction as to kind, was taken to represent the nutritive 
value, and the hay values were computed in proportion to them. 

1 Compare Henneberg, fiber den Heuwert der Futterstoffe ; Beitrage zu Futter- 
ung der Wiederkauer, Heft i, i860, pp. 1-16; and von Gohren, Naturgesetze der 
Fattening, 1872, pp. 286-305. 

591 



592 NUTRITION OF FARM ANIMALS 

The system had the advantage of simplicity. Experience had 
afforded a fairly definite idea of the quantity of hay required 
for a given amount of production. It was only necessary to 
compute from the hay values what weights of the available 
feeding stuffs would produce equal effects. The simplicity of 
the calculations, due especially to the fact that the relative 
value of a feed was expressed by a single fixed number, led to 
a rapid adoption of the system. " To each feeding stuff a defi- 
nite hay value was assigned and in a short time one had a 
beautiful table constructed which gave the most exact infor- 
mation regarding the value of the most diverse feeding materials 
in comparison with hay. Anything which appeared in any way 
suited for feeding found its place in the table and each new 
feeding stuff which the progress of agronomy provided, directly 
or indirectly, was likewise quickly incorporated. It went so 
far that even the salt supplied to the animals was computed in 
hay values." * 

Thaer himself based his figures in part on the results of prac- 
tical experiments. Numerous subsequent investigators carried 
out direct comparisons of feeding stuffs on an extensive scale 
and not one but several tables of hay values were formulated. 
Unfortunately, these tables differed widely from each other, 
some of them giving two or three times as great a hay value as 
another to the same feed. It was evident also that the un- 
limited substitution of different classes of feeds, as for instance 
of grain or roots for hay, was impossible. Such discrepancies 
and limitations led to various modifications of the methods of 
estimating the hay values. Boussingault regarded the protein 
content of the feed as the principal factor, while Nathusius took 
into account also the content of crude fiber and Wolff 2 worked 
out a somewhat elaborate method in an attempt to retain the 
convenience of reckoning with a single number for a feed. The 
impossibility of this, however, gradually came to be recognized, 
and the hay values have now only a historical interest. 

701. Practical feeding trials. — But while the system of 
hay values has become obsolete the idea of determining the 
relative nutritive values of feeding stuffs on the basis of direct 
comparisons of the results obtained in practice has survived in 

1 Settegast, Die Fiitterungslehre, 1879, p. 4. 

2 Die landwirtschaftliche Fiitterungslehre, 1861, pp. 455-456. 



RELATIVE VALUES OF FEEDING STUFFS 593 

full vigor. A very considerable share of the investigations in 
stock feeding during the last two decades, especially perhaps in 
the United States, has consisted of experiments intended to 
determine the effects of the substitution of one feed for another 
in a ration. 

Undoubtedly the so-called practical trial has an important 
part to play in the development of a sound theory of feeding as 
well as in relation to the economic aspects of the subject. Re- 
garded, however, simply as a means for the quantitative deter- 
mination of the relative values of feeding stuffs it is subject to 
precisely the same limitations and uncertainties as the old at- 
tempt to determine hay values, and in this respect has in 
general led to scarcely more satisfactory or concordant results. 
It is as true in the later as in the earlier experiments that 
the effect of a feeding stuff may vary widely with the com- 
bination in which it is fed and the conditions under which 
it is used. 

702. Feed units. — An interesting attempt to revive the 
fundamental conception of hay values in a modified form and 
within a restricted field, and thus to retain the advantage of 
expressing the relative value of a feed by a single number, 
is found in the so-called feed unit system devised by Fjord 
and his associates in Denmark and extensively used also in 
Sweden. 1 

The feed unit system, like that of hay values, is essentially a 
system of empirical equivalents according to which feeding 
stuffs may replace each other. Instead of hay, the basis of 
comparison is a unit weight of grain (corn, barley, wheat or 
rye or a mixture of grains). This is called a feed unit and the 
amounts of other feeds required to equal the feed unit have 
been determined in very extensive cooperative feeding experi- 
ments by the group system (572) with swine and especially with 
dairy cows. The experiments themselves have been executed 
with every precaution to ensure accuracy. The results for 
dairy cows, as revised by Woll for American feeding stuffs, 
and the Danish values for swine and for the horse are given by 
Henry and Morrison 2 as follows : — 

1 For a more complete discussion of the feed unit system compare Woll; Wis- 
consin Expt. Sta., Circular No. 37. 

2 Feeds and Feeding, 15th Edition, p. 127. 

2Q 



594 



NUTRITION OF FARM ANIMALS 



Table 167. — Amount of Different Feeds Required to Equal One 

Feed Unit 1 



Feed 



FOR DAIRY COWS 

Concentrates 

Corn, wheat, rye, barley, hominy feed, dried 
brewers' grains, wheat middlings, oat shorts, 
peas, molasses beet pulp, dry matter in roots . 

Cottonseed meal 

Oil meal, dried distillers' grains, gluten feed, soy- 
beans 

Wheat bran, oats, dried beet pulp, barley feed, 
malt sprouts 

Alfalfa meal, alfalfa molasses feeds 

Hay and straw 

Alfalfa hay, clover hay 

Mixed hay, oat hay, oat and pea hay, barley and 
pea hay, red-top hay 

Timothy hay, prairie hay, sorghum hay . . . 

Corn stover, stalks or fodder, marsh hay, cut straw 
Soiling crops, silage and other succulent feeds 

Green alfalfa 

Green corn, sorghum, clover, peas and oats, can- 
nery refuse 

Alfalfa silage 

Corn silage, pea vine silage 

Wet brewers' grains 

Potatoes, skim milk, buttermilk 

Sugar beets 

Carrots 

Rutabagas 

Field beets, green rape 

Sugar beet leaves and tops, whey 

Turnips, mangels, fresh beet pulp 

The value of pasture is generally placed at 8 to 10 
units per day, on the average, varying with 
kind and condition 



Feed Required to 
Equal i Unit 



Average 



1.0 

0.8 
0.9 

I.I 

1.2 
2.0 



Range 



i-5- 3-0 



2.5 


2.0- 3.0 


3-° 


2-5- 3-5 


4.0 


3-5- o-o 


7.0 


6.0- 8.0 


8.0 


7.0-10.0 


5-o 


— 


6.0 


5.0- 7.0 


4.0 


— 


6.0 


— 


7.0 


— 


8.0 


— 


9.0 


8.0-10.0 


10.0 


— 


12.0 


— 


12.5 


10.0-15.0 



1 The values for pigs and horses are those given in the Danish valuation table 
and those for dairy cows the values as revised by Woll for American feeding stuffs 
in Wisconsin Circular, No. 37. 



RELATIVE VALUES OF FEEDING STUFFS 



595 



Table 167. — Amount of Different Feeds Required to Equal One 

Feed Unit {Continued) 



Feed 


Feed Requeued to 
Equal i Unit 




Average 


Range 


FOR PIGS 

Indian corn, barley, wheat, oil cakes .... 
Rye, wheat bran 


I.O 

1.4 

4.0 

6.0 

I2.o 


— 










Whey 




FOR HORSES 

One pound of Indian corn equals one pound of 
oats or one pound of dry matter in roots . . 





703. Logical basis of feed unit system. — The Scandinavian 
feed unit values have a broad experimental basis. The re- 
sults of the experiments have been reasonably consistent 
and in general the feed unit values correspond well with the 
relative net energy values discussed in the following chapter 
except that they ascribe somewhat higher values to protein- 
rich feeds. 

Nevertheless, the logical basis of the system has the same 
defect that is inherent in all such systems. As was shown in 
Chapter V (263), feed has two distinct functions and these func- 
tions are incommensurable. It is as impossible to combine the 
value of a feed as a source of protein or other structural material 
with its value as a source of energy, and to express the result in 
a single number, as it is to compare the relative values of food 
and water to a starving man. A protein-rich feed like cotton- 
seed meal, for example, will necessarily produce a greater effect 
when added to a ration deficient in protein than when added 
to one containing an abundance of that ingredient; with a 
material deficient in protein precisely the reverse would be true. 
As a matter of fact the feed units are only claimed to be equiva- 
lent values, " under ordinary conditions of feeding these animals, 
when fed in mixed rations that would contain over a certain 



596 NUTRITION OF FARM ANIMALS 

minimum of digestible protein." x As Henry and Morrison have 
pointed out, " The feed unit system has been evolved in a com- 
paratively small region where similar crops are grown on the 
different farms and the price of purchased feeds does not vary 
widely throughout the district." 

704. Comparison of feed units and net energy values. — 
The writer is not able to agree with those who would introduce 
the feed unit system in this country with its wide variety 
of feeding stuffs and conditions. The applicability of the feed 
units, as just pointed out, is conditioned upon the presence 
of sufficient protein in the rations. As thus limited, however, 
they practically attempt to measure the relative values as sources 
of energy, and for this purpose the use of the net energy values 
to be considered in the next chapter is just as simple arithmeti- 
cally and equally accurate, while it has two immense advantages. 
First, the net energy values are rational and not empirical values. 
They are based on physiological investigations and their very 
imperfections tend to stimulate further investigation which may 
lead to their great improvement or to the discovery of new and 
still better methods of comparison. The feed unit, on the other 
hand, constitutes a dead end so far as investigation is concerned, 
leading to nothing beyond some increase in numerical accuracy, 
while it is far inferior in pedagogic value. Second, the feed 
units are purely relative values, based on direct comparisons of 
the results with different materials with no attempt to discover 
the causes of the observed differences. They show to what 
extent one feeding stuff is better or worse than others, but es- 
tablish no relation between feed and product. Energy values, on 
the other hand, aim to show the amount of product which may 
be expected from a unit weight of the feeding stuff — i.e., the 
amount of energy which it can contribute to the maintenance 
of the body or to the building up of new tissue. Thus, if aver- 
age maize meal, for example, has an energy value of 85 Therms 
per hundred pounds, this means that one hundred pounds of it, 
fed as part of a maintenance ration, would conserve in the body 
of the animal an amount of fat and protein having an energy 
value of 85 Therms, which would otherwise be burned up to 
support the vital activities. Furthermore, it means that, if 
added to the maintenance ration, the maize will furnish ma- 

1 Woll, loc. cit. p. 13. 



RELATIVE VALUES OF FEEDING STUFFS 597 

terial sufficient to produce a quantity of milk or of meat having 
an energy value of 85 Therms. Still further, the investigations 
by which these facts are established also show that out of the 
approximately 187 Therms gross energy of 100 pounds of maize 
meal, about 50 escape unused in the various excreta, while about 
52 are expended in the various processes connected with the 
consumption and assimilation of the feed. In other words, they 
show the nature of the losses suffered as well as the final amount 
of product to be expected. Such data as these have an inde- 
pendent value and are of an entirely different nature from those 
expressed in the feed units. 

§ 2. Relative Values Based on Composition and 
Digestibility 

705. Chemical composition. — Even before the rise of the 
system of hay values, attempts were made by Davy, Einhof, 
Sprengel and others to compare feeding stuffs on the basis of 
chemical analyses, and indeed the earlier hay values were 
based in part on such comparisons (700). The methods for 
the chemical analysis of feeding stuffs were gradually improved, 
although they still remain quite imperfect, but along with this 
improvement came a clearer recognition of the fact that the 
problem of relative values is at bottom a physiological and not 
a chemical question. 

706. Physiological functions of nutrients. — In particular 
the teachings of Liebig and the investigations of Bischoff and 
Voit x on the nutrition of carnivora served to establish those 
basal facts regarding the functions of proteins, carbohydrates, 
fats and ash in nutrition which. have been confirmed and ex- 
tended by later investigations and have been outlined in Chap- 
ter V. Haubner appears to have been the earliest to suggest the 
application of these principles to comparisons of feeding stuffs 
and the feeding of farm animals, while to Grouven 2 belongs the 
credit of having first formulated the requirements of animals 
and the values of feeding stuffs in terms of the different classes 
of nutrients. His tables, however, were based on the total 
nutrients found by chemical analysis and were comparatively 

1 Gesetze der Ernahrung des Fleischfressers, i860. 

2 Vortrage iiber Agriculturchemie, 1858. 



598 



NUTRITION OF FARM ANIMALS 



soon replaced by more accurate data based on determinations of 
the digestible nutrients. 

707. Henneberg's and Stohmann's investigations. — It is to 
the fundamental investigations of Henneberg and Stohmann 1 
at the Weende Experiment Station, near Gottingen, that we 
are indebted for the inauguration of a system of comparing the 
values of feeding stuffs which has endured with little material 
change up to the present time. These investigators were the 
first to apply systematically in studying the nutrition of herbiv- 
ora the physiological principles already demonstrated for other 
classes of animals and to base their determinations upon the 
outgo as well as upon the income of the body. Their earlier 
experiments deal chiefly with the digestibility of feeding stuffs 
and rations. Later a comprehensive scheme of investigation, 
including determinations of the gaseous excreta, was laid out 2 
and begun but never completed. 

Table 168. — Example of Computation of Digestible Nutrients 



Chemical composition 

Water 

Ash 

Protein 

Non-protein 

Crude fiber 

Nitrogen-free extract . . 
Ether extract 



Percentage digestibility 

Ash 

Protein 

Non-protein 

Crude fiber 

Nitrogen-free extract . . . 
Ether extract 



Clover Hay 



Digestible nutrients 

Ash 

Protein 

Non-protein 

Crude fiber 

Nitrogen-free extract . . 
Ether extract 



15-03 
5-49 

10.24 
1.36 

28.61 

36.98 
2.29 



46.48% 
53-19% 
100.00% 
50.27% 
68.94% 
65.02% 



5.49X0.4648= 2.55% 
10.24 X 0.5319 = 5.45% 

1.36 X 1. 000 = 1.36% 
28.61 X 0.5027 = 14-38% 
36.98 X 0.6894 = 25.49% 

2.29 X 0.6502 = 1.49% 



Maize Meal 



13-73 
125 
8.80 
0.25 
1.89 

70.44 

364 

100.00 



18.40% 

66.43% 
100.00% 
32.40% 
97-75% 
95-74%) 



1.25 X 0.1840 = 0.23% 
8.80 X 0.6643 = 5-85% 
0.25 X 1.000 = 0.25% 
1.89 X 0.3240 = 0.61% 
70.44 X 0.9775 = 68*.85% 
3.64 X 0.9574 = 3-48% 



1 Beitrage zur Begrundung einer rationellen Futterung der Wiederkauer, i860 
and 1864. 

a Neue Beitrage, etc., 1870. 



RELATIVE VALUES OF FEEDING STUFFS 



599 



708. The digestible nutrients. — The methods of digestion 
experiments as used by Henneberg and Stohmann and modified 
by later experimenters were outlined in Chapter III (157-161). 
A vast number of determinations of digestibility have been 
made, upon a great variety of materials, and the results have 
served as the basis for computing the relative values of feeding 
stuffs. The method of comparison may be illustrated by 
means of the digestion experiment on clover hay and maize 
meal used in Chapter III to illustrate the method. (Table 168.) 

Simplified statement. — Since the digestible crude fiber and 
digestible nitrogen-free extract have been shown (168, 169) to 
have the elementary composition of starch, they have been 
commonly added together and called carbohydrates. Con- 
sidering the digestible ether extract to be substantially fat, 
and omitting the ash on the assumption that an average 
ration contains a sufficient supply, the amounts of the three 
principal groups of digestible nutrients may be stated more 
concisely as follows : — 

Table 169. — Simplified Statement of Digestible Nutrients 



Clover 
Hay 



Maize 
Meal 



Digestible protein . . 
Digestible non-protein . 
Digestible carbohydrates 
Digestible fats . . . 



5-45% 

1.36% 

39-87% 

i-49% 



5-8 5 % 

0-25% 

69.46 % 

3-48% 



This statement may be still further simplified. A pound 
of fat produces when burned about 2.25 times as much heat as 
the same weight of carbohydrates. The non-proteins have ap- 
proximately the same heat value as the carbohydrates, while 
it is still questioned whether they help to build up protein tis- 
sue. By multiplying the digestible fat by the factor 2.25 and 
adding the digestible carbohydrates and non-protein we obtain 
the carbohydrate equivalent for the digestible matter other 
than protein and the digestible nutrients may be expressed in 
the following still more concise form : — 



6oo 



NUTRITION OF FARM ANIMALS 



Table 170. — Digestible Nutrients Reduced to Carbohydrate 

Equivalent 



Digestible protein 

Digestible carbohydrates equivalent to non-nitrog- 
enous nutrients 

Total nutrients 



Clover 
Hay 




50.03 % 



Maize 
Meal 



5-85% 

77-54% 
83-39% 



709. The nutritive ratio. — By the method just illustrated 
the content of a feeding stuff in digestible matter is expressed 
by two numbers which correspond to the two functions of the 
nutrients already described (263) . The digestible protein shows 
what the feeding stuff can contribute towards the structural 
needs of the body, while the carbohydrate equivalent of the 
digestible non-nitrogenous nutrients shows what portion of the 
digestible nutrients can serve only as a source of fat or of energy. 
The ratio between these two quantities gives a useful indication 
as to whether a feeding stuff or mixture of feeding stuffs is suited 
for forms of production like growth or milk production, which 
require a considerable supply of protein, or whether it is better 
adapted for those which, like work or fattening, make special 
demands for fuel material. This so-called " nutritive ratio " 
(better, nutrient ratio) is obtained by a simple proportion. Thus 
in the two instances just given, it is computed as follows, the 
second half of the proportion constituting the nutritive ratio : — 

For clover hay, 5.45 : 44.58 = 1 : 8.2 
For maize meal 5.85 : 77.54 = 1 : 13.3 

710. Significance of results. — Under the stimulus of Hen- 
neberg and Stohmann's pioneer work and under the leadership 
of Wolff, investigation of the digestibility of feeding stuffs 
was actively taken up in Germany and later in the United 
States and other countries, and as the result of much labor ex- 
pended during the last fifty years a fairly complete knowledge 
of the amounts and proportions of the digestible nutrients sup- 
plied by most of the ordinary feeding stuffs has been accumu- 
lated. Extensive tables of averages have been published by 



RELATIVE VALUES OF FEEDING STUFFS 601 

various authors, including many of the agricultural experiment 
stations, and it is an easy matter for the feeder to learn what 
amounts and kinds of digestible nutrients any given feed or 
ration will supply. 

In view of the extensive use of such tables it is important 
that the exact significance of the results which they embody 
should be understood. As a mere matter of logical concep- 
tion, the comparison of feeding stuffs on the basis of their 
digestible nutrients is inferior to that based on hay values or 
on feed units. In these methods the attempt is made, how- 
ever crudely, to compare the actual effects produced by the 
feeding stuffs in the animal body. A determination of diges- 
tibility, on the contrary, affords no direct information whatever 
as to the nutritive effect of the materials digested. It is not 
even necessary to weigh the animal in a digestion trial. The 
comparison of feeding stuffs on this basis is between what they 
contain and not between what they accomplish. 

Nevertheless, tables of digestible nutrients have been of great 
value in promoting more rational and profitable feeding, but it 
is becoming increasingly evident that they express but part of 
the truth. The essential feature of the newer methods of 
comparison outlined in this volume is not that they employ 
units of energy as a basis of comparison but that they con- 
stitute a return to the logical conceptions which were at the 
basis of the early methods and which were discussed in so il- 
luminating a manner by Henneberg and Stohmann in the 
introduction 1 to their " Neue Beitrage " in 1870. These 
newer methods seek to determine, by more elaborate and 
accurate methods than were available to the earlier experiment- 
ers, the actual effect of the feed on the body of the animal as 
well as its content of matter and energy. 

§ 3. Conditions Affecting Digestibility 

711. Digestibility variable. — Not only is the current method 
of estimating the relative values of feeding stuffs, as described in 
the previous section, based largely on the digestibility of the ma- 
terials in question, but the latter is also a most important fac- 

1 Uber das Ziel und die Methode der auf den landwirtschaftlichen Versuchs- 
stationen auszufuhrenden thier-physiologischen Untersuchungen. 



602 NUTRITION OF FARM ANIMALS 

tor in determining the actual production values discussed in the 
next chapter, since, as there shown (742), the excretion in the 
feces constituted the greatest, although not the only, loss of 
chemical energy suffered by the feed. 

The percentage digestibility of a feeding stuff or of its several 
constituents, however, has not a fixed and invariable value, 
analogous to the solubility of a chemical compound, but may be 
affected more or less by a variety of conditions, although to a 
less extent than is frequently supposed. This arises from the 
fact noted in Chapter III (155) that portions of ingredients 
capable per se of solution and resorption in the digestive tract 
actually escape digestion for various reasons and reappear in 
the feces. Any conditions which influence the digestibility in 
this way, however, necessarily affect the value of the feeding 
stuff by whichever method determined, and the more impor- 
tant of them may be conveniently considered in this connection. 

The conditions which affect, or which are supposed to affect, 
the degree of completeness with which the potentially digestible 
ingredients of a feeding stuff are actually digested may be di- 
vided into those relating to the animal itself and those relating 
to the feed. 

Conditions relating to the animal 

712. Variation at different times. — An important fact, 
which must be borne in mind in studying the influences of 
various factors upon digestion, is that the percentage digesti- 
bility of the same feeding stuff by the same individual has been 
found to vary more or less at different times. 

This has been shown especially by G. Kiihn. 1 In experiments 
upon the digestibility of meadow hay by cattle the variations in the 
percentage digestibility of the dry matter, which is the one least sub- 
ject to error, ranged from o.6 to 2.1, averaging 1.3, and the digestibility 
of the organic matter showed about the same variations. That for 
the nitrogen-free extract averaged 1.8, while in the case of the crude 
fiber, protein and ether extract it reached 3.3. These variations were 
shown to be materially larger than the possible errors of experiment. 
Similar, although relatively somewhat smaller, variations were ob- 
served on rations of hay and bran. Moreover, Kiihn points out that 
the maximum differences were found in those cases in which the larger 

1 Landw. Vers. Stat., 29 (1883), 129, 147 and 153. 






RELATIVE VALUES OF FEEDING STUFFS 603 

number of single trials were made. No connection could be traced 
between the variations in digestibility and the condition of the animals. 

The writer L observed a similar difference in two experiments upon 
one sheep with clover hay while the other sheep of the pair showed 
no significant difference. In later experiments 2 in which the feces 
of three steers were quantitatively collected daily for periods of 56 
and 27 days on identical rations, it was shown that the digestibility 
of the air dry matter 3 and nitrogen computed from overlapping ten- 
day periods, varied at times from the average for the whole experi- 
ment by amounts greater than the estimated experimental error. 
Mumford, Grindley, Hall and Emmett 4 likewise observed distinct 
fluctuations in the digestion coefficients obtained with cattle in suc- 
cessive weekly periods following preliminary periods of from two to 
four weeks. 

All the foregoing experiments were upon dry feed and the writer 
is inclined to attribute them, to a considerable degree at least, to irreg- 
ular voiding of the feces. 

713. Species. — The differences in the anatomy of the di- 
gestive organs of different species might naturally be expected 
to result in differences in the extent to which the feed of these 
species is digested. This is true especially of those ingredients 
of the feed whose so-called digestibility is due to the action of 
organized ferments and which, . therefore, will be more or less 
dependent upon the opportunities which the digestive tract 
affords for the stagnation of the feed and so for the activity 
of these organisms. 

714. Species of ruminants. — Few direct comparisons of 
the digestibility of the same feeding stuff by different species 
of ruminants are on record. In view of the similarity of the 
alimentary canal in these species, one would naturally expect 
to find comparatively small differences in the extent to which 
identical feeding stuffs are digested. In a general way this 
expectation is borne out by the average results of a large number 
of recorded digestion experiments upon feeds bearing the same 
name, although not of identical composition. Thus Wolff, 5 
in 1874, compared the results of about 40 German experiments 

1 Amer. Jour, of Science, 28 (1885), 368. 

2 Penna. Expt. Sta., Bui. 42 (1898), pp. 129-141. 

_ 3 The daily excretion of dry matter was not determined and there is a possi- 
bility of a small error due to lack of exact uniformity in the air drying. 

4 Ills. Expt. Sta., Bui. 172 (1914). B Landw. Fiitterungslehre. 



604 NUTRITION OF FARM ANIMALS 

on cattle and sheep and Jordan and Hall l have made similar 
comparisons of nine American experiments. 

On the basis of comparisons of this sort it has been generally 
considered that digestion coefficients obtained with one species 
of ruminants may be applied to others without material error 
and the sheep or goat has been the favorite experimental an- 
imal. Such direct evidence as is available, however, leads to 
some modification of this conclusion. 

Comparisons of the digestive powers of cattle and sheep for 
identical feeding stuffs have been reported by Frear, 2 the Missis- 
sippi Station, 3 Bartlett, 4 Kellner, 5 Tangl and Weiser, 6 Zuntz, 7 
and Voltz. 8 

The experimental results, while not extensive and not al- 
together consistent, seem, when taken in connection with the 
general comparisons previously made, to warrant the conclu- 
sion that as regards the better grades of roughages the differ- 
ence in digestive power between cattle and sheep is not marked 
and, with the exception of Zuntz's rather remarkable results, 
the same would seem to be the case as regards concentrates. 
On the other hand, it would appear that in the case of the coarser 
and less digestible forms of forage a distinct difference exists in 
favor of cattle. Kellner is inclined to ascribe this difference to 
the greater percentage of water in the contents of the lower 
intestine of cattle as compared with sheep, which favors a more 
extensive action of the organized ferments. 

715. The horse compared with ruminants. — A number of 
comparisons have been made of the digestibility of identical 
feeding stuffs by horses and by sheep as representing ruminant 
animals. The most extensive trials of this sort were made by 
Wolff 9 in Hohenheim from 1877 to 1884 but Tangl and Weiser 10 
have also compared the digestibility of several samples of 
hay by horses and by sheep or cattle and Langworthy 11 has 
compiled the results of a large number of digestion experiments 

1 U. S. Dept. Agr., Office Expt. Stas., Bui. 77 (1900), 90. 

2 Penna. Expt. Sta., Rep. 1890, 58. 3 Eighth Rpt. (1895), 79. 

'Maine Expt. Sta., Bui. no (1904). 5 Landw. Vers. Stat., 63 (1906), 313. 

6 Landw. Jahrb., 35 (1906), 205. 

7 Jahrb. Ver. Spiritus Fabrikanten in Deutschland, XII (1912), 324. 

8 Landw. Jahrb., 45 (1913), 422. 

9 Grundlagen fiir die rationelle Futterung des Pferdes, 1886. 
10 Landw. Jahrb., 35 (1905), 159. 
11 U. S. Dept. Agr., Office Expt. Stas., Bui. 125, p. 44. 



RELATIVE VALUES OF FEEDING STUFFS 605 

Table 171. — Digestibility by Sheep and by Horses 



ROUGHAGE 

Wheal straw * 

Sheep 

Horse 

Meadow hay — inferior 

Sheep 

Horse 

Meadow hay — average 

Sheep 

Horse ....... 

Meadow hay — superior 

Sheep 

Horse 

Dried pasture grass 

Sheep 

Horse 

Red clover hay 

Sheep 

Horse 

Alfalfa hay 

Sheep 

Horse 

Oats 

Sheep 

Horse 

Beans 

Sheep 

Horse 

Peas 

Sheep 

Horse 

Lupins 

Sheep 

Horse 

Maize 

Sheep 

Horse 



Number 

of 
Experi- 
ments 



10 
6 

2 

I 



12 

6 

13 



Percentage Digestibility 



Dry 
Mat- 
ter 



45 
20 

57 
47 

56 

47 

62 
5o 

65 

54 

55 
5i 

58 
58 

70 
66 

87 
85 



77 



7i 



90 



Organic 
Matter 



23 

59 

47 

59 

48 

64 
5i 

76 
62 

56 
5i 

59 

58 

7i 
68 

90 
87 

90 

80 



72 



9i 



Crude 
Pro- 
tein 



54 
57 

57 
57 

65 
62 

73 
69 

56 
56 

7i 

73 

80 



87 
86 

89 
83 



94 

79 
78 



Crude 

Fiber 



59 

27 

68 
39 

56 
36 

63 

42 

80 
57 

50 
37 

45 
40 

30 
21 

79 
65 

66 



97 
5i 

62 
100 



Nitro- 
gen- 
free 
Extract 



37 
18 

62 

56 

62 
55 

65 

57 

76 
66 

61 
63 

66 
70 

76 

74 

9i 
93 

93 
89 

78 
5i 

9i 
94 



Ether 
Ex- 
tract 



46 
23 

51 
24 

54 
20 

65 
13 

56 
29 

4i 
14 

83 
7i 

84 
13 

75 
7 

78 
27 

85 
63 



1 Results regarded by Wolff as of questionable accuracy. 



606 NUTRITION OF FARM ANIMALS 

on both horses and rilminants. The results of Wolff's com- 
parisons are contained in Table 171. 

In general, the comparisons have shown a distinct superiority 
of ruminants over horses in the digestion of roughages, especially 
as regards those ingredients (crude fiber and nitrogen-free ex- 
tract) whose so-called digestion is wholly or in part a fermenta- 
tion. Even in the better grades of forage the crude fiber was 
on the whole considerably less digestible by horses than by 
ruminants, although three of Tangl's experiments are excep- 
tions, while less difference appears as regards the nitrogen-free 
extract and scarcely any as regards the crude protein. On the 
other hand, little difference was observed in most cases in the 
digestibility of the total organic matter and nitrogen-free extract 
of concentrates. In the latter the digestibility of the crude 
fiber was also relatively low but in view of its small amount and 
the consequent uncertainty in the results little significance 
attaches to this difference. The notably lower figures for the 
digestibility of the ether extract by horses arise in all probability 
from a larger excretion of ether-soluble excretory products 
in the feces of these animals rather than from any real differ- 
ence in digestibility. 

716. Swine compared with ruminants. — Comparisons of 
the digestibility of identical feeds by swine and by sheep have 
been reported by Honcamp, Neumann and Milliner, 1 the feed- 
ing stuffs being wheat, rye and the by-products of their milling. 
Although the results upon the individual animals of the same 
species fluctuated somewhat, as is not unusual (718), the aver- 
age results showed no material superiority on the part of either 
species. 

Owing to the small percentage of crude fiber contained in the 
feeds, the results upon this ingredient are naturally quite variable 
and of no especial significance. Aside from this, there seems to have 
been a slight superiority on the part of the swine in the case of the 
rye products (with the exception of the germ) , while with the wheat 
products the reverse was the case, especially with the coarser milling 
products. The swine seem to have digested the crude protein fully 
as well as the sheep in all the experiments. 

Fingerling, Bretsch, Losche and Arndt, 2 in experiments de- 
signed especially to test the relative digestive powers of sheep and 

1 Landw. Vers. Stat., 81 (1913), 205. - 2 Ibid., 83 (1913), 181. 



RELATIVE VALUES OF FEEDING STUFFS 607 



swine for crude fiber, added straw pulp, young grass and wheat 
chaff to basal rations. Their average results were as follows : 

Table 172. - Digestibility by Sheep and by Swine 



Dry 
Mat- 
ter 



Straw pulp 

Sheep 

Swine 

Grass 

Sheep 

Swine 

Wheat chafi 

Sheep 

Swine 



% 

72.65 
101.22 

65.29 
49-58 

40.33 
20.53 



Or- 
ganic 
Mat- 
ter 



% 

73-!9 

88.85 

69.77 
51-86 

46.93 
22.95 



Crude 
Pro- 
tein 



% 



76.85 
5 2 -OS 

55.56 



Crude 
Fiber 



Nitro- 
gen- 
Free 
Ex- 
tract 



Ether 
Ex- 
tract 



77.27 
94.81 

69.49 
39-39 

3°-34 



% 

72.23 
63-75 

67.29 

52.07 

51-54 

27.86 



% 



66.93 
84-35 



The amount of straw pulp added to the basal ration was com- 
paratively small, so that the results on this material are sub- 
let to relatively large errors (161), but the conclusion seems 
indicated that pure cellulose, freed from encrusting matter, can 
be readily digested by swine, and this conclusion is ; fuly sup- 
ported by the later determinations of Fingerlmg Kohler and 
Reinhardt. 1 For the crude fiber of ordinary feeding stuffs, 
on the contrary, the digestive power of the swine was decid- 
edly inferior to that of the sheep. . 

A general idea of the relative digestive power of swine and 
ruminants may also be gained by a comparison of the average 
results obtained for the two species on feeding stuffs of the same 
name although not of identical composition, as shown ^by com- 
pilations hlJ those by Kellner - and by Henry and Morrisom 
The recorded results do not indicate that there is any material 
difference between swine and ruminants as regards their di- 
gestive power for concentrates. As in the case of the horse, 
there seems to be a tendency toward a lower percentage diges- 
tibility of ether extract by swine, due most likely to the presence 

1 Landw. Vers. Stat., 84 (1914). U9- 

2 Ernahrung landw. Nutztiere, 6th Ed., p. 45- 
» Feeds and Feeding, 15th Ed., pp. 647-652. 



6o8 



NUTRITION OF FARM ANIMALS 



of more ether-soluble excretory products in the feces of these 
animals. The figures for the crude fiber of concentrates are 
also materially lower with swine in some cases, but in others 
equal to or even higher than those obtained for ruminants. In 
view of the small percentage of crude fiber in the concentrates 
and the corresponding range of possible error, however, the 
results on this point are of little significance. The crude fiber 
of roughage is but imperfectly digested by swine. Crude pro- 
tein would appear, on the whole, to be rather more completely 
digested by swine than by ruminants, possibly indicating the 
presence of more nitrogenous excretory products in the feces 
of the latter. 

717. Fowls compared with swine. — Owing to the difficulty 
of collecting the feces of fowls separately from the urine, com- 
paratively few determinations upon these animals have been 
made. Bartlett, 1 who has reported a number of such experi- 
ments, gives the following as the average digestion coefficients 
obtained in all recorded experiments up to 1910. 

Table 173. — Digestibility by Fowls 



Bran, wheat . , 

Beef scrap . , 
Beef (lean meat) 

Barley . . . . 

Buckwheat . . 
Maize, whole 

Maize, cracked . 

Maize . . . , 

Clover . . . . 

India wheat . . 

Millet . . . . 

Oats . . . . 

Peas . . . , 

Wheat . . . , 

Rye 

Potatoes . . , 



Number 

of 
Experi- 


Organic 
Matter 


Crude 
Protein 


Nitro- 
gen-free 
Extract 


ments 










% 


% 


% 


3 


46.70 


71.70 


46.00 


2 


80.20 


92.60 


— 


2 


87.65 


90.20 


— 


3 


77.17 


77-32 


85.09 


2 


69.38 


59-4o 


86.99 


16 


86.87 


81.58 


91.32 


2 


&3-3° 


72.20 


88.10 


2 


83.10 


74.60 


86.00 


3 


27.70 


70.60 


14.30 


3 


72.70 


75.00 


83.40 


2 


— 


62.40 


98.39 


13 


62.69 


7I-3 1 


90.10 


3 


77.07 


87.00 


84.80 


10 


82.26 


75-Q5 


87.04 


2 


79.20 


66.90 


86.70 


6 


78.33 


46.94 


84.46 



Ether 
Extract 



% 
37.00 
95.00 
86.30 
67.86 
89.22 
88.11 
87.60 
87.60 
35-50 
83.80 

85.71 
87.89 
80.01 
53-oo 
22.60 



1 Maine Expt. Sta., Bui. 184, 1910. 



RELATIVE VALUES OF FEEDING STUFFS 609 

Crude fiber appears to be relatively difficult of digestion by 
fowls and the results obtained upon this ingredient were vari- 
able and apparently capricious. Aside from this, a comparison 
of results with those for swine shows quite a close general 
agreement between the two classes of animals. 

718. Individuality. — In addition to the specific differences 
just considered, differences have likewise been observed in the 
digestibility of the same feeding stuff by individuals of the 
same species. To some extent this may be due to abnormal- 
ities, such as defective teeth or chronic diseases of the digestive 
organs, but in normal animals distinct individual differences 
also seem to occur. 

In their compilation of the results of American digestion ex- 
periments, Jordan and Hall 1 were unable to find conclusive 
evidence of such differences in digestive power and are inclined 
to attribute the apparent variations which were observed largely 
to the variability at different times already considered (712). 
The experiments by G. Kiihn, 2 however, which were cited in 
the discussion of the latter possibility, seem also to afford in- 
dubitable instances of individual differences in cattle and the 
same is true of experiments by the writer 3 in which three 
grade Shorthorn steers were under observation at different times 
for five years. Carmichael, Newlin and Grindley 4 have like- 
wise observed significant differences in the digestive powers of 
individual pigs. On the other hand, Christensen and Simpson 5 
made three series of digestion trials on alfalfa hay for two suc- 
cessive years, using four range steers each year, and failed to find 
any consistent individual differences. 

The existence of time variations in digestibility (712) renders 
it somewhat difficult to decide whether an observed difference 
in the digestion of the same feeding stuff by two animals is really 
an expression of individuality or whether it is in a sense acci- 
dental. A comparison based on a single digestion trial as or- 
dinarily made is liable to be misleading, and to secure correct 
results requires either a number of trials or a trial extend- 
ing over a longer period than is ordinarily employed. On the 

1 U. S. Dept. Agr., Office Expt. Stas., Bui. 77 (1900), 88. 

2 Landw. Vers. Stat., 29 (1883), 129, 147, 153. 

3 Penna. Expt. Sta., Bui. 42 (1898), 124. 

4 Science, July 2, 1915, p. 38. 5 New Mexico Expt. Sta., Bui. 91 (1914). 

2 R 



610 NUTRITION OF FARM ANIMALS 

whole, however, the conclusion seems justified that animals of 
the same species may differ to some extent in their digestive 
power but that these individual differences are probably less 
than appear to be indicated by the results of single digestion 
trials and are certainly much too small to account in any degree 
for the economic differences in animals. Even the differences 
observed in the results of short digestion trials rarely exceed 
three or four per cent and are usually materially less than this. 

719. Breed. — The foregoing facts are sufficient of them- 
selves to render improbable the existence of any considerable 
breed differences as regards digestion, and this conclusion has 
been confirmed by the experiments of Haubner and Hofmeister, 1 
of Wolff 2 and of Armsby and Fries. 3 The recorded data 
taken together fail to indicate any material difference in the 
digestive power of different breeds or between pure-bred and 
scrub animals. 

There exists a somewhat general impression that animals 
which show themselves superior as producers of meat, milk, 
etc., whether as the result of breed, heredity, or of individual 
variation, owe that superiority, in part at least, to a superior 
digestive power ; that is, it is supposed that the improved breeds 
of farm animals and the superior individual animals within a 
breed are able to extract more nutriment from a given weight 
of a feed than can inferior animals. The reasons for the un- 
doubted economic superiority of some individuals over others 
have been considered in previous chapters. So far as differ- 
ences in digestive power are concerned, however, the experimen- 
tal evidence gives little support to the popular impression. 

720. Age. — Comparisons of the digestive power of the 
same animals (lambs) at different ages were made by Wolff 4 
in 1871-72 which led to the conclusion that between the ages of 
six and fourteen months the percentage digestibility of the 
feed remained practically unchanged and this conclusion is 
confirmed by the results of an experiment by Weiske 5 under- 
taken primarily for another purpose. 

721. Work. — Investigations on the effect of the performance 
of work upon the digestibility of rations have naturally been 

1 Landw. Vers. Stat., 12 (1869), 8. 2 Landw. Jahrb., 1 (1872), 533. 

3 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128. 

4 Landw. Jahrb., 2 (1873), 221. 5 Ibid., 9 (1880), 205. 



RELATIVE VALUES OF FEEDING STUFFS 6ll 

made upon the horse. Experiments upon this subject have 
been reported by Wolff and his associates at Hohenheim and by 
Grandeau and LeClerc at Paris. 

Wolff's 1 experiments were upon a single animal, a draft horse 
weighing about 550 kgs. (1200 pounds). The ration remained 
the same in all the periods and was insufficient to maintain the 
weight of the animal in the periods of heavier work. The 
work was that of draft, done at a slow walk (about 1.9 miles 
per hour) with in most instances a draft of 60 kgs., the total work 
per day (not including that of locomotion) ranging from 475,000 
to 1,800,000 kilogram meters. Under these conditions, no 
effect on the digestibility of the mixed rations employed was 
observed. 

Grandeau and LeClerc's investigations 2 were made upon 
several different horses of the Paris Cab Company and in- 
cluded experiments upon work and others upon simple loco- 
motion both at a walk and a trot together with rest ex- 
periments. 

The plan of the experiments differed from that of Wolff's 
in some important particulars. The animals used were lighter 
(about 400 kgs. as compared with 550 kgs.) and apparently of 
a more active temperament as indicated by their more rapid 
walk, the velocity of which varied from 2.6 to 3.0 miles per 
hour. The work, which was that of draft, was done on a dyna- 
mometer similar to Wolff's. The draft was about half of that 
of Wolff's experiments and the total amount of work 3 was 
considerably less, ranging in most cases from 400,000 to 600,000 
kilogram meters per day, with a maximum in one experiment of 
785,000. Its amount was approximately the same in all the 
experiments in each series and was not greater at a trot than 
at a walk. 4 Finally, corresponding to the main purpose of the 
experiment, which was to study the feed requirements of cab 
horses, the rations in the periods of work or of walking exercise 
were heavier than in those in the periods of rest, the increase 
being one-tenth in the experiments on locomotion and, in most 
cases, one-half in the experiments on work. The proportions 

1 Landw. Jahrb., 8, Ergzbd. I (1879), 73 ; 16, Ergzbd. Ill (1887), 53-71. 
2 L'alimentation du cheval de trait; Berger-Levrault et cie, 1882-89. 

3 Not including that of locomotion. 

4 The total work in the former case was, of course, somewhat greater on account 
of the greater expenditure of energy in trotting as compared with walking (664). 



6l2 NUTRITION OF FARM ANIMALS 

of the different feeding stuffs in the rations, however, remained 
the same, except in a very few cases. 

On the whole, and despite some irregularities in the results 
on single ingredients, Grandeau and LeClerc's results agree 
with Wolff's in showing that work even at a somewhat rapid 
walk does not materially affect the digestibility of rations. On 
the other hand, they show a distinct decrease of the percentage 
digestibility in the periods in which the work was done at a 
trot. It scarcely seems that this effect can be ascribed to the 
work as such, since the measured amount was less than in Wolff's 
experiments and was not greater at a trot than at a walk. More- 
over, mere horizontal locomotion at a trot, in some instances at 
least, seems to have produced the same effect, which apparently 
is due to the difference in gait. It is true that the rations were 
heavier in the work periods and that this (722) may possibly 
have affected the digestibility, but no reason is apparent why 
it should have produced a greater effect in the trotting periods 
than in the walking periods. 

The influence of work has also been investigated in a different way 
by Tangl 1 and by Scheunert. 2 A weighed amount of oats was fed 
after 36 hours of fasting and the animal was killed from one to five 
hours later and the contents of the stomach and small intestines 
weighed and analyzed. On the assumption that none of the crude 
fiber of the oats was digested in this portion of the alimentary tract, 
the results show that work delays the passage of the feed from the 
stomach to the intestines, especially during the first one or two hours. 
As a consequence, the gastric juice penetrates the larger mass of the 
feed more slowly and more of it is neutralized by the saliva, so that 
the stage of starch digestion is prolonged and that of protein diges- 
tion shortened, the result being that more carbohydrates and less pro- 
tein are digested. In the later stages of digestion the differences tend 
to equalize themselves, while the effect of work upon the intestinal 
digestion was found to be small. Scheunert computes that the total 
digestibility was considerably increased by the performance of work. 
As noted, however, the results cover only the first five or six hours 
of digestion. The method of comparison is confessedly an approxi- 
mate one and the results show very considerable variations among 
themselves. Only actual digestion experiments suffice to decide the 
question of the total effect of work upon digestion. 

1 Arch. Physiol. (Pfliiger) ; 65 (1896), 545. 

2 Arch. Physiol. (Pfliiger) ; 109 (1005), 145; Landw. Jabrb., 34 (1905), 805. 






RELATIVE VALUES OF FEEDING STUFFS 613 



Conditions relating to the feed 

722. Quantity of feed. — Current methods of computing 
rations regard the digestibility of feeding stuffs as unaffected 
by. the amounts consumed. As regards exclusive feeding 
with roughage, the results of a considerable number of ex- 
periments by various investigators appear to justify this view. 
With mixed rations of roughage and concentrates fewer ex- 
periments have been made, but the results indicate a distinct 
decrease in the percentage digestibility when the amount of 
the ration is increased considerably above that required for 
maintenance. 

Roughage. — The early experiments of Henneberg and Stohmann on 
cattle include several cases in which varying amounts of clover and 
meadow hay were fed and in which the digestibility was substantially 
unaffected by the quantity consumed, and the same was found to be 
true by Wolff at Hohenheim in a number of experiments on sheep. 1 
Later comparative experiments by the same investigator 2 on sheep 
and horses have confirmed his earlier results, as have also those of 
Tangl and Weiser 3 upon sheep fed alfalfa hay or alfalfa silage, while 
Miintz and Girard 4 likewise found no distinct effect of the quantity 
consumed upon the digestibility of alfalfa hay by the horse. In 
three experiments by Armsby and Fries 5 on each of two steers a sub- 
maintenance ration of timothy hay was slightly better digested than 
a maintenance ration in five cases out of six, but the differences were 
small, amounting to from 1.0 to 2.7 per cent on the dry matter. 
Later unpublished experiments have given similar results. In earlier 
experiments 6 by the same authors on different amounts of clover hay, 
practically no differences were observed. 

Mixed rations. — Kellner 7 obtained the following results in four 
periods in which varying amounts of a mixed ration consisting of 
meadow hay, dried molasses beet pulp, rye bran and cottonseed meal 
were fed to cattle. 

1 Compare Wolff, Die Ernahrung der landwirtschaftlichen Nutztiere, pp. 63 
and 64. 

2 Landw. Jahrb., 1 (1872), 533; Landw. Vers. Stat., 21 (1878), 19. 

3 Landw. Vers. Stat., 74 (1911), 277 and 282. 

4 Centbl. Agr. Chem., 27 (1898), 756. 

5 U. S. Dept. of Agri., Bur. Anim. Indus., Bui. 128 (1911), p. 27. 

6 U. S. Dept. of Agri., Bur. Anim. Indus., Bui. 74 (1905), pp. 12-13; Bui. No. 
101 (1908), pp. 11-13. 

7 Ernahrung landw. Nutztiere, 6th Ed., p. 49. 



6 14 NUTRITION OF FARM ANIMALS 

Table 174. — Effect of Amount of Mixed Ration Consumed on 

Digestibility 





Daily 
Ration 


Digestibility 




Organic 
Matter 


Crude 
Protein 


Crude 
Fiber 


Nitrogen- 
free 
Extract 


Ether 
Extract 


Period I . . . . 
Period II ... . 
Period III . . . 
Period IV . . . 


Kgs. 
10.84 
13.OI 

15.18 
10.84 


% 

76.I 

74-7 
72.8 

75-8 


% 
71.0 
68.3 
65.8 
71.2 


% 
62.8 
61.2 

59-2 
62.6 


% 
82.O 
80.8 
79.O 
8l.2 


% 

63-5 
64.4 
64.2 
67.6 



Eckles 1 determined the digestibility of mixed rations sufficient 
for maximum milk production, and thirteen months later, when the 
cows were dry, that of a maintenance ration of the same mixture of 
feeding stuffs. About thirty per cent of the dry matter of the ration 
was derived from hay, thirty-six per cent from silage and thirty-four 
per cent from grain. 

Table 175. — Digestibility of Mixed Rations by Cows 







Dry 


Percentage Digestibility 




Mixed 


Matter 
Eaten 






Ration 












per 
Head 


PER 

IOOO 

Live 
Weight 2 


Organic 
Matter 


Crude 
Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


Ether 
Ex- 
tract 


Cow No. 27 


Kgs. 














Full ration .... 


24-95 


3I-30 


66.3 


58.8 


538 


72.6 


67.O 


Maintenance ration . 


8.71 


10.95 


73-8 


67-3 


55-3 


82.I 


73-2 


Cow No. 62 
















Full ration .... 


15-88 


19.88 


67.0 


60.6 


53-9 


73-6 


59-8 


Maintenance ration . 


7.62 


9-58 


72.2 


65-5 


52.1 


81.0 


73-9 



Mumford, Grindley, Hall and Emmett 3 determined the digestibil- 
ity of four different mixed rations of hay and grain by four pairs of 
cattle receiving respectively slightly more than a maintenance ration, 
one-third feed, two-thirds feed and full feed. One animal of the full- 
fed pair showed a distinctly lower digestive power than the other in 
all the periods and the same was true of one animal receiving the 
two-thirds feed in the last two periods. The results upon the other 
animal in this case are shown in the table in parenthesis : — 



Mo. Expt. Sta., Research Bui. 4. 



2 Approximate. 



3 Ills. Expt. Sta., Bui. 172 (1914). 



RELATIVE VALUES OF FEEDING STUFFS 615 

Table 176. — Digestibility of Dry Matter by Cattle 





Period i 


Period 2 


Period 3 


Period 4 


Average 


Ratio of hay to 












grain .... 


1 : 1 


1: 3 


1 : 5 


1: 5 






Per Cent 


Per Cent 


Per Cent 


Per Cent 


Per Cent 


Maintenance . . 
One-third feed 
Two-thirds feed 
Full feed .... 


69.9 

67.12 

65.62 

63.03 (64.50) 


77.28 
72.06 
69.07 
64.56 (69.64) 


78.79 

75-74 

73-62 (75-57) 

70.11 (74.81) 


79-99 
77-14 

75.10 (77-8o) 
76.12 (79-53) 


76.51 
73.02 

70.83 (72.02) 
68.46 (72.12) 



In these experiments the digestibility of the maintenance ration 
appears to have been distinctly higher than that of the heavier rations 
in Period 1, in which the largest proportion of hay was fed. The 
differences became much less marked as the total feed was progres- 
sively increased, and as between the two-thirds and full-feed ration 
was scarcely significant, especially in view of the individual differ- 
ences in this pair. The effect also decreased as the proportion of 
grain in the ration was increased, so that on the average of the four 
periods but little difference is shown with certainty among the three 
heavier rations. 

Unpublished experiments by Armsby and Fries, in which varying 
amounts of a uniform mixture of two-thirds grain and one-third hay 
were fed to steers, afford confirmation of the foregoing results : — 

Table 177. — Digestibility of Mixed Rations by Steers 



Steer C 
Period 2 
Period 3 

Steer E 
Period 1 
Period 2 
Period 3 

Steer 
Period 1 
Period 2 
Period 3 



Amount 

of 
Mixed 
Ration 



Kgs. 

2-55 
1.80 



3-75 
2.04 

1-45 



5-4 
3-2 
1.9 



Dry 

Matter 
Eaten 
per 
1000 
Live 
Wt. 



8.26 
5.83 

15-74 
8.58 
5-04 

15-25 
9-36 
5-59 



Percentage Digestibility 



Organic 
Matter 



68.8 
74-9 

68.9 

75-i 
74.1 

68.4 
72.1 
74.2 



Crude 
Protein 



67.2 

73-7 

66.9 
65.2 
68.1 

65.0 
66.9 
70.2 



Crude 
Fiber 



25.2 
39-5 

40.6 
49.9 
44-7 

35-6 
37-o 
40.4 



Nitro- 
gen-free 
Extract 



79.2 
83-4 

76.3 
83.O 
82.4 

76.7 
8l. I 

82.7 



Ether 
Extract 



75-7 
78.9 

70.6 
78.0 
78.4 

77.6 
80.6 
80.0 



6i6 



NUTRITION OF FARM ANIMALS 



One would naturally be inclined to ascribe the lower diges- 
tibility of heavier rations to their greater bulk and relatively 
more rapid passage through the digestive tract, and in part to 
the consequent lessened extent of the bacterial fermenta- 
tions. It would seem that on liberal rations material poten- 
tially digestible and resorbable may thus escape digestion and 
appear in the feces. Some of the reasons for this have al- 
ready been indicated in discussing the feces as a feed residue 
(155). The presence of considerable amounts of undigested 
grains or fragments of grain in the feces of heavily fed animals 
is readily demonstrated by washing out the finer portions, but 
actual digestion experiments to determine the extent of this 
loss have not yet been reported. 

723. Excess of carbohydrates. — It has been established by 
numerous experiments that an undue proportion of carbohy- 
drates in a ration tends to reduce its digestibility, especially by 
ruminants. The effect is most distinct when pure digestible car- 
bohydrates are added to a ration, but is manifest also when large 
amounts of feeding stuffs rich in carbohydrates are introduced. 

An example of the former is afforded by an experiment by 
G. Kuhn 1 on two oxen. It was divided into three periods, in 
the first of which the animals received a daily ration of 9 kgs. 
of hay to which, in the second and third periods, 2 kgs. and 3.5 
kgs. of starch, respectively, were adcfed. Assuming the starch 
to have been completely digested 2 the following amounts of 
the several ingredients were computed to have been digested 
from the hay by Ox V. 

Table 178. — Nutrients Digested from Hay, with and without 

Starch 



Period 



I 

II 

III 



No starch 

2 kgs. of starch 

3.5 kgs. of starch 



Dry 
Matter 


Organic 

Matter 


Crude 
Pro- 
tein 


Crude 
Fiber 


Nitro- 
gen- 
free 
Extract 


Grams 


Grams 


Grams 


Grams 


Grams 


4549 


4378 


451 


1572 


23 x 5 


4317 


4161 


407 


1475 


2239 


3914 


3746 


301 


1392 


2016 



Ether 
Ex- 
tract 



Grams 
40 
41 
38 



1 Landw. Vers. Stat., 44 (1894), 470-472. 

2 No starch could be detected microscopically in the feces. 



RELATIVE VALUES OF FEEDING STUFFS 617 

Exnressed in another way, the feces in Periods II and III 
coined the following amonnts of hay ingredients which , ac- 
cordme to the results of Period I, must be regarded as digestible 
but which under the influence of the addition of starch escaped 
digestion. 



Table 179. - DtoEsxiBLE Nutrients or Hav Escaping in Feces 




Period 



II 
III 



2 Kgs. starch 
3.5 Kgs. starch 



Dry 

Matter 



Grams 



232 
635 



Matter 



Grams 



Pro- 
tein 



NlTRO- I £ THER 
ORGANIC ^f CRTOE GJW- Ex . 

Fiber free tract 
, Extract 

Grams I Grams I Grams 

76 I •- I 



217 
632 



Grams 

44 
15° 



180 



299 



The foregoing is a typical example of the results of numerous 
siir ^erimtnts on' ruminants in which ^«t, 
substances and even cellulose have been added to hay ana to 
mted rations. Other things being equal, the magnitude of the 
effect has usually increased, as in ^»^*X 
tity of carbohydrates added. Its total amount has vara d con 

Jerably in different f*^™£*££%?Z& 
has been uniformly the same. This constitutes tne 
« depression of digestibility," since, of course e diges ion 
coefficients are lowered by the escape of potential MgJ 
matter in the feces. It should be noted, however, that in some 
of theseTn stances more or less of the added carbohydrate (starch) 
ha itself escaped digestion. According to ««*£»££ 
Wolff, 1 swine appear to be much less sensiU ve to tins influence 
of carbohydrates than are ruminants and a few ^ s «™ 
by Grandeau and Alekan • seem to indicate that the same 

^Feeing st^rich in carbohydrates, as well as such ma- 
terial Is starch or sugar, may apparently nkewi* : = ade- 
crease of digestibility, although the quantitative r lations can 
not always be so clearly followed as m ^™"£j U ™ 
carbohydrates. Thus six experiments with beet molasses by 

iLandw. Vers. Stat., 19 (1876), 273. ' T 

> Jahresber. Agr. Chem., 49 (1906), 350; Ann. Sci. Agron., 1904, I, 30, 33c 



6i8 



NUTRITION OF FARM ANIMALS 



Lehmann l and one by Kellner 2 showed that this substance, 
like the pure carbohydrates, caused a depression in the di- 
gestibility of all the ingredients of a basal ration, but in two 
later trials by Kellner 3 the only effect was on the digestibility 
of the crude fiber. 

The question has been especially investigated, however, by 
Wolff in regard to the feeding of tubers and roots. Heavy feed- 
ing of these materials is generally stated, on the strength of his 
experiments, to result in a pronounced decrease in the diges- 
tibility of the remainder of the ration, although, as Wolff him- 
self points out, the evidence is by no means conclusive. 

In Wolff's extensive series of experiments on sheep 4 increasing 
quantities of roots or potatoes were fed along with hay whose diges- 
tibility had been previously determined, and it was found that as the 
amount of roots added to the ration was increased, the feces contained 
increasing amounts of undigested nutrients. For example, in one 
experiment with meadow hay and sugar beets, the percentage digesti- 
bility of the hay, computed on the assumption that the sugar beets 
were completely digestible, was as follows : — 

Table 180. — Computed Percentage Digestibility of Hay with and 

without Sugar Beets 





Dry 

Matter 


Organic 
Matter 


Crude 
Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


Ether 
Extract 


Fed alone . . . 
Fed with sugar beets 


% 

55-9 
43-9 


% 

59-2 
50.0 


% 

57-6 
51.0 


% 
55-2 
5i-9 


% 
62.1 

50.0 


% 
60.0 
29.4 



What seems a more reasonable method of comparison, however, 
is to compute the digestibility of the roots in the first instance on 
the assumption of unaltered digestibility of the hay, just as in the 
case of concentrates (161) and to see whether the coefficients thus ob- 
tained show any decrease as the proportion of roots fed is increased. 
Wolff has carried out the computation in this manner for his entire 
series of experiments, numbering in all no single trials. The aver- 

1 Landw. Jahrb., 25 Erzgbd. II (1896), 117. 
2 Landw. Vers. Stat., 53 (1900), 199. 
3 Ernahrung landw. Nutztiere, 5th Ed., pp. 158-175. 
4 Landw. lahrb., 8 Ergzbd. I (1879), 123. 



RELATIVE VALUES OF FEEDING STUFFS 619 

age results for total organic matter and for nitrogen-free extract are 
fairly uniform in each series of experiments, although there was some- 
what more variation in the individual trials, and fail to give any- 
decided indication of a diminished digestibility with the increasing 
amounts of roots consumed. The computed digestibility of the crude 
protein is more or less variable, but on the whole a decreased diges- 
tibility of this ingredient as the proportion of roots to hay increased 
seems to be plainly shown. 

It is, of course, impossible to determine in a digestion experi- 
ment in which roots are added to a basal ration what propor- 
tion of the fecal matter is derived from the roots and what from 
the remaining ingredients, and such results as those of Wolff 
may be interpreted either as showing a fairly constant diges- 
tibility of both the hay and the roots (aside from crude protein), 
or, on the assumption of complete digestibility of the roots, as 
showing a progressive depression in the digestibility of the 
hay. To the writer, the former appears on the whole the more 
reasonable course, although it should be added that in some of 
the experiments the absolute amount of crude fiber in the feces 
was increased by an amount greater than that contained in the 
roots consumed, thus demonstrating a depression of the diges- 
tibility of this constituent of the hay. Probably the truth 
lies between the two views. It is unlikely that roots are en- 
tirely digestible and, on the other hand, it is probable that a 
large proportion of them may diminish to some extent the di- 
gestibility of other feeding stuffs consumed with them. It is 
to be remembered, however, that roots contain not altogether 
inconsiderable quantities of crude protein which, as shown in a 
following paragraph (727), tends to offset the effects of their 
carbohydrates. 

725. Cause of diminished digestibility of protein. — Atten- 
tion has already been called (163-167) to the influence of the 
excretory products contained in the feces on the apparent diges- 
tibility of the nutrients and especially of protein. According 
to Kellner's and Pfeiffer's results, the digestion of each 100 
grams of dry matter, whether protein or nitrogen-free material, 
results in the excretion in the feces of approximately 0.4 gram 
of nitrogen in the form of these excretory products. If, then, 
a kilogram of dry starch be added to a basal ration, the nitrog- 
enous excretory products in the feces are increased by ap- 



620 NUTRITION OF FARM ANIMALS 

proximately 25 grams, so that apparently 25 grams less of pro- 
tein is digested from the basal ration, while in reality the true 
digestion may not have been affected. Thus in Kiihn's exper- 
iment with hay and starch (723) the nitrogenous excretory 
products corresponding to the 1646 grams dry matter of the 
2 kgs. of starch consumed, would be approximately 40 grams, 
while the excess actually found was 44 grams, the difference 
being insignificant. 

The agreement is by no means always so close as in this 
instance and in none of the experiments on the addition of car- 
bohydrates which have been cited was the true digestibility 
(166) of the protein determined. Nevertheless, the general 
conclusion seems justified that at least the larger part of the 
influence of carbohydrates and of feeding stuffs rich in car- 
bohydrates on the apparent digestibility of the protein of the 
feed is due to the fact that, when added to a basal ration, they 
increase the nitrogenous excretory products in the feces. On 
the other hand, however, it must be remembered, that while 
the true digestibility may not be lowered, it is, as already 
pointed out (167), the apparent digestibility which measures 
the real advantage derived by the animal from the digestion 
of its feed. Whether the increased excretion of nitrogenous 
matter in the feces after carbohydrate feeding be due to an 
apparent or a real depression of digestibility, or to both com- 
bined, it is none the less a loss of protein from the body. 

In general the depression in the percentage digestibility of 
the protein is greater the poorer the basal ration is in this in- 
gredient. As Kellner * has pointed out, however, this does 
not justify the statement frequently made that the magnitude 
of the depression is dependent upon the nutritive ratio of the 
feed. The difference is purely a mathematical one. A de- 
crease of the digestibility of the protein by 50 grams, for ex- 
ample, is relatively very much greater in a basal ration of oat 
straw, containing only 140 grams of apparently digestible crude 
protein than in a basal ration of meadow hay containing 430 
grams of digestible protein. 

The fact that the addition of protein tends to decrease the 
apparent digestibility of the protein of a basal ration is also 
readily explicable from this point of view. Pfeiffer's exper- 

1 Landw. Vers. Stat., 44 (1894), 344. 



RELATIVE VALUES OF FEEDING STUFFS 621 

iments (162) showed that the increase in the nitrogenous ex- 
cretory products in the feces was about the same whether the 
added digestible matter consisted of carbohydrates or of protein. 
Consequently, the addition of protein to a ration would tend 
to diminish the apparent digestibility of the protein just as 
would the addition of carbohydrates. 

The non-proteins, especially when given in the form of green 
vegetable material and roots, likewise increase the nitrogen con- 
tent of the feces, but a review of the literature of the subject l 
shows that, as in the case of the proteins, the increase consists, 
at least in large part, of metabolic products and does not indicate 
any decrease in the true digestibility of the protein, although 
it does, of course, decrease the amount available to the organism. 
726. Cause of diminished digestibility of carbohydrates. — - 
The depression of digestibility of the non-nitrogenous ingredi- 
ents of the feed of ruminants appears to be due to an entirely 
different cause, viz., to a modification in the fermentation pro- 
cesses in the rumen, and the fact that these effects are observed 
chiefly on this class of animals lends strong support to this view. 
It has already been stated (128-132) that the disappearance 
of more or less of the comparatively insoluble carbohydrates of 
the feed during its passage through the alimentary tract is due, 
particularly in ruminants, to a bacterial fermentation, occur- 
ring principally in the first stomach and yielding chiefly carbon 
dioxid, methane and organic acids. Furthermore, it has been 
shown that when the more soluble carbohydrates, like starch 
and sugar, are introduced into the ration they are attacked by 
the organisms and undergo the same fermentation, yielding cor- 
responding amounts of the characteristic gaseous product, 
methane. It can scarcely be doubted that the decreased di- 
gestibility of the less soluble carbohydrates under these cir- 
cumstances is due to a partial diversion of the activity of the 
ferment organisms to the maltose resulting from the action of 
the saliva on the starch or to the sugar directly added, since 
these substances are presumably more readily attacked than 
cellulose and the like. 

The action of nitrogenous substances in counteracting this 
effect of an excess of readily soluble carbohydrates is plausi- 
bly explained as due to its supplying more nitrogenous food 

» Compare U. S. Dept. of Agr., Bur. Anim. Indus., Bui. 139- 



62 2 NUTRITION OF FARM ANIMALS 

for the organisms and so stimulating their multiplication and 
activity, and the fact that readily soluble nitrogenous materials 
like amino acids or ammonium salts seem to be particularly 
effective is quite in harmony with this view. The action of 
nitrogenous materials in stopping the excretion of undigested 
starch, on this view, would be explained as due to an increase 
of the proportion fermented, leaving less to be acted on by the 
digestive juices of the intestines. 

727. Effect of addition of protein. — It was shown in the 
last paragraph that rations containing a large portion of car- 
bohydrates and therefore relatively deficient in protein, i.e., 
those having a wide nutritive ratio, are likely to show an im- s 
paired digestibility, especially by ruminants. Correcting this 
condition by increasing the protein content of such rations tends, 
as would be expected, to increase their digestibility. 

Trials have been made by several investigators of the effect of 
the addition of nearly pure protein (wheat gluten with 78 per 
cent of crude protein, or fish meal with 96 per cent of crude 
protein in the organic matter) to a basal ration. In general, 
such an addition has had little effect on the digestibility of the 
protein of the basal ration, but in several experiments on rumi- 
nants an increased digestibility of crude fiber, and, in some cases 
of the nitrogen-free extract, has been observed, especially, with 
basal rations poor in protein. In other instances, however, 
particularly when the deficiency in protein was less marked, 
this effect has been either slight or entirely absent and the 
same is true of such experiments on swine as have been thus 
far reported. Experiments are also on record in which the 
addition of feeding stuffs rich in protein, such as oil cake or 
legumes, has distinctly increased the digestibility of the crude 
fiber of a basal ration and others in which such an addition 
has stopped an excretion of undigested starch in the feces. 

728. Effect of non-protein. — The addition to the basal ra- 
tion of ruminants of digestible non-protein in the form of plant 
extracts as a rule tends to diminish the apparent digestibility 
of the protein of the basal ration, i.e., to increase the excretion 
of nitrogen in the feces, while the simpler forms of non-protein, 
such as asparagin or ammonium salts, have not usually pro- 
duced this effect. 1 

1 Compare U. S. Dept. Agr., Bur. Anim. Indus., Bui. 139 (191 1), pp. 14-28. 



RELATIVE VALUES OF FEEDING STUFFS 



623 



On the other hand, the effect of protein in increasing the di- 
gestibility of the non-nitrogenous ingredients of rations contain- 
ing an excess of carbohydrates is shared also by the non-pro- 
teins, such comparatively simple substances as asparagin or 
even ammonium salts having in a number of instances exerted 
a marked influence of this sort. 

729. Influence of drying. — The simple removal of water 
from a feeding stuff affects its digestibility but slightly. Weiske * 
compared the digestibility of green and dried alfalfa and espar- 
cet by sheep. In these experiments the forage was mowed 
daily, one-half of it fed and the other half dried without loss, 
which was a comparatively easy task with the relatively small 
amounts to be handled. In the second half of the experiment 
the portions of dried forage were fed to the same animals in the 

Table 181. — Percentage Digestibility of Forage, Green and Dried 





Total 
Organic 
Matter 


Crude 

Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


Ether 
Extract 


Ash 


Weiske 














Alfalfa 














Green .... 


67.40 


83.08 


45-15 


72.79 




51.46 


Dried .... 


66.69 


82.73 


44-83 


71.71 




5I-30 


Difference . . 


— 0.71 


- o-35 


- 0.32 


- I.08' 




— 0.16 


Esparcet 














Green .... 


66-35 


72.50 


42.16 


78.29 


66.68 


50.21 


Dried .... 


62.12 


69.98 


36.40 


74-35 


66.24 


45-59 


Difference . . 


- 4-23 


- 2.52 


- 5-76 


- 3-94 


- 0.44 


— 4.62 


Armsby and 














Caldwell 














Grass 














Green .... 


68.87 


65.66 


74-37 


73.18 


54-73 


SO-05 


Dried .... 


71-31 


71.66 


76.78 


72.95 


60.06 


55-56 


Difference . . 


+ 2.44 


+ 6.00 


+ 2.41 


- 0.23 


+ 5-33 


4-5-Si 


MORGEN 














Grass 














Green .... 


66.4 2 


69.6 


65.6 


77-8 


65.6 


30.7 


Dried .... 


63.42 


55-7 


66.3 


73-8 


66.3 


12.5 


Difference . . 


- 3-o 2 


- 3-9 


+ 0.7 


- 4.0 


+ 0.7 


- 18.2 



1 Jour, f . Landw., 25 (1877), 170. 

2 Total dry matter. 



624 



NUTRITION OF FARM ANIMALS 



same order that the green forage was. Armsby and Caldwell 1 
subsequently made a similar experiment upon a cow by sub- 
stantially the same plan, using mixed grasses cut while still 
young and corresponding substantially to pasture grass, and 
Morgen 2 has reported comparisons of the same sort on three 
sheep. The average results of the four comparisons are shown 
in Table 181. While the earlier experiments are open to 
criticism in some particulars, on the whole the conclusion ap- 
pears warranted that the digestibility of forage is not very 
materially diminished by the simple removal of water and that 
the lower value of ordinary dry roughage as compared with green 
forage is largely due to differences in maturity and composition. 
730. Cutting of roughage. — The digestibility of coarse fod- 
ders is not increased by cutting, and, indeed, it would be dif- 
ficult to conceive how that process could have such an effect, 
since in either case the feed is comminuted during mastication 
to practically the same extent. This is strikingly shown in 
experiments by Kellner 3 in which the preparation of straw 
and chaff was carried to the extent of grinding it to a fine meal. 
Table 182 shows his comparison between wheat straw and barley 
straw cut into inch and a half lengths or finely ground. 

Table 182. — Digestibility Cut and Finely Ground 





Organic 
Matter 


Crude 

Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


Ether 
Extract 


Wheat straw 
Cut 

Barley straw 

Cut 

Finely ground 


% 

35-8 
34-8 

49.8 
48.9 


% 

-18.3 
— 21.6 

34-4 
19.1 


% 
44.0 
41.9 

52.9 
52.6 


% 
30.8 
30-7 

50.0 
49.4 


% 
16.7 
39-2 

32.5 
36-9 



731. Grinding of grain. — The outer coats of seeds are re- 
sistant to solvents, their purpose being to protect the seeds from 
external influences. When whole grain is fed, especially in large 

iPenna. Expt. Sta., Rpt. 1888, p. 60; Agricultural Science, 3, 295. 

2 Landw. Vers. Stat., 75 (1911), 321. 

3 Ernahrung landw. Nutztiere, 6th Ed. p. 266. 



RELATIVE VALUES OF FEEDING STUFFS 625 

amounts to greedy feeders or to animals with imperfect teeth, 
more or less of it escapes mastication and, protected by the 
outer coats, passes through the digestive tract relatively unacted 
upon. Such apparently intact grains of corn, oats, etc., still 
capable of germination, are a familiar sight in the droppings of 
heavily fed animals. 

Such visible losses, however, are not confined to the feeding 
of whole grain but, although less obvious, extend to cracked or 
crushed grain as well. If, for example, the feces of full-fed 
cattle receiving cracked corn or other grain be washed out, a 
considerable amount of fragments of grain may be recovered, 
the amount depending upon the total quantity fed and the con- 
sequent rapidity with which it passes through the digestive 
tract. Moreover, it is evident that the mechanical separation 
by washing is necessarily imperfect. Not only may the sieve 
hold back other things than fragments of grain, but it is like- 
wise clear that any undigested fragments of the latter which 
are smaller than the meshes of the sieve will pass through and 
be lost, so that fine meal or well-masticated grain might suffer 
a greater loss through incomplete digestion than would be 
indicated by such tests. While it is to be supposed that smaller 
fragments will undergo more rapid solution in the digestive 
tract than larger ones, it is evident that the rapidity of passage 
through the organs is an important factor and that even com- 
paratively small bits may, under some circumstances, escape 
complete digestion, while on the other hand, with light feeding, 
whole grain might be almost as well digested as when ground. 
Qualitatively, the results reached by washing out the feces are 
of great interest, but they may readily be misleading as regards 
' the actual advantage of grinding. 

Surprisingly few investigations upon the relative digesti- 
bility of ground and unground grain have been reported. Jor- 
dan and Hall, 1 in their compilation of American digestion ex- 
periments up to 1900, present two comparisons with horses 
and two with swine, all of which show the ground grain to be 
more digestible than the unground, the difference with respect 
to the dry matter ranging from 3.3 to 14 per cent. 

Gay, 2 in experiments upon oats with a horse weighing about 

1 U. S. Dept. Agr., Office Expt. Stas., Bui. 77, P- 97- 
2 Centbl. Agr. Chem., 25 (1896), 729. 



2 s 



626 



NUTRITION OF FARM ANIMALS 



340 kilograms (750 lb.) and receiving per day 3 kilograms of 
oats and 2 kilograms of hay, obtained the following results : — 

Table 183. — Percentage Digestibility of Oats by a Horse 



Whole .... 
Crushed . . . 
Ground . . . 

Gain by crushing 

Gain by grinding 



Dry 

Matter 


Ash 


Crude 
Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


64-53 


27.78 


71.30 


42.00 


74.70 


68.58 


31-97 


79-15 


48.87 


74-99 


72.73 


42.71 


94.11 


63.60 


75-19 


4.05 


4.19 


7.85 


6.87 


0.29 


8.20 


14-93 


22.81 


21.60 


0.49 



Ether 
Extract 



40.90 
59-46 
54.78 

18.56 

13-88 



While the results just cited are more or less variable, and 
while the small differences in the digestibility of the nitrogen-free 
extract in Gay's experiments seem peculiar, the results as a 
whole clearly show an increased digestibility by swine and 
horses as a result of grinding, while they also show that the 
difference is apparently not very great — less perhaps than 
would have been expected. 

Gay also reports the following results of similar experiments 
upon a sheep weighing 81 kilograms and eating 500 grams of 
oats and 750 grams of alfalfa hay: — 

Table 184. — Percentage Digestibility of Oats by a Sheep 





Dry 

Matter 


Ash 


Crude 
Protein 


Crude 
Fiber 


Nitro- 
gen-free 
Extract 


Ether 
Extract 


Whole 

Crushed .... 
Ground .... 


66.24 
66.60 
67.03 


36.68 

26.55 
27.14 


73-03 
74.62 

73-59 


45-55 
45-Q3 
44-75 


74.10 

78.55 
76.99 


58.31 
64.81 
72.20 



With the exception of the ether extract, whose digestibility 
it is difficult to determine accurately (165), the percentage 
digestibility is practically identical in the three cases. So far 
as a single experiment goes, therefore, it indicates that there is 
no advantage in grinding oats for sheep. Experiments upon 



RELATIVE VALUES OF FEEDING STUFFS 627 

other ruminants and with other feeding stuffs are lacking, but 
it does not appear surprising that a ruminant should digest 
whole grain more completely than a non-ruminant. As a 
whole, the results upon the influence of grinding on digestibility 
are comparatively meager and in particular they afford no in- 
formation as to the effect of variations in the amount fed upon 
the relative digestibility of whole grain and of coarse or fine 
meal. 

732. Acids. — The extensive use of silage lends interest to 
the question of the influence of acids on the digestibility of 
feeding stuffs. 

Weiske l compared the digestibility of meadow hay with and 
without the addition of sulphuric acid (0.75 per cent SO3) by one 
sheep, using two periods on each ration, and obtained almost 
absolutely identical results, with the exception of a slight in- 
crease in digestibility of the ash and ether extract of the acidified 
hay. Kellner 2 added a much larger proportion of lactic acid 
(2.67 per cent) to a ration of hay and maize fed to a sheep and 
likewise observed practically no effect on the digestibility. 

Apparently, then, such amounts of organic acids as are or- 
dinarily consumed in silage and other feeds are without effect 
on digestion in the case of ruminants and this conclusion is to 
a certain extent supported by the general results of experiments 
which have shown that ensiled forage is fully as digestible as 
the same material carefully dried. The amounts of acid con- 
sumed under normal conditions are after all not large as com- 
pared with the quantities produced in the rumen and neutral- 
ized by the saliva. That excessive amounts of acids may 
stimulate peristalsis and so produce scouring is doubtless true, 
and it may be presumed that other species, such as the horse, 
for example, may be more sensitive to acids than ruminants. 

733. Condiments. — One of the exaggerated claims made 
for the various proprietary condimental feeds is that they are 
able to increase materially the digestibility of rations to which 
they are added. Not the slightest scientific basis for this claim 
exists. All experimenters agree that they are without influence 
in this respect. Recent investigations by Fingerling, 3 for ex- 
ample, in which fennel, anise, fenugreek and malt sprouts were 

1 Jour. Landw., 33 (1885), 21. 2 Ernahrung landw. Nutztiere, 6th Ed., p. 56. 
3 Landw. Vers. Stat., 62 (1905), 41-57. 



628 NUTRITION OF FARM ANIMALS 

added both to ordinary feeds and to a ration made up of ab- 
normally flavorless materials showed no effect upon the per- 
centage digestibility. 

734. Water drinking. — Stress has been laid by numerous 
writers on the supposed effect of water drinking on digestion, 
particularly by the horse. It has been asserted that drinking 
after feeding tends to dilute the gastric juice and to wash the 
feed out of the stomach and the feeder has been advised to 
water his animals before feeding rather than after feeding. 

Even were the supposed facts true, it is questionable whether 
the conclusions drawn would be warranted, since the stomach, 
far from being the sole organ of digestion, serves largely as a 
sort of preliminary reservoir (119), and the extensive intestines 
of farm animals afford ample opportunity for the digestion of 
any substances which may escape action in the stomach. As 
a matter of fact, however, no such washing out or degree of 
dilution occurs as has been supposed. As has already been 
stated (131), the contents of the stomach are semi-solid rather 
than liquid and, as shown by their stratification, much less 
mixing of them takes place than is sometimes imagined. Scheu- 
nert l has shown that in the horse the larger part of the water 
drunk passes along the walls of the stomach and around its 
contents and is quite promptly discharged into the small 
intestine. This is especially the case when the stomach is 
well filled with feed. In the contrary case more water is 
retained, but in no case did the total- dilution of the entire 
stomach contents exceed about io per cent. Moreover, the 
water which enters the duodenum is rather rapidly resorbed 
and has no material effect in the transportation of feed into the 
large intestine. 

In view of these facts it is not surprising to find that the 
few digestion trials which have been made show no evidence of 
a decrease in digestibility as a result of drinking after eating. 

Gabriel and Weiske 2 in experiments on two sheep found no signifi- 
cant difference in the percentage digestibility of a ration of oats and 
hay, whether the water was given before or after feeding or kept con- 
stantly before the animals. The percentage digestibility of the 
organic matter was: — 

1 Arch. Physiol. (Pfliiger), 144 (1912), 411 ; 151 (1913), 396. 

2 Landw. Vers. Stat., 45 (1895), 311. 



RELATIVE VALUES OF FEEDING STUFFS 



629 



Water constantly before the animals 
Watered before feeding . . . . 
Watered after feeding . . . . . 



Sheep II 




Tangl, 1 in a number of experiments upon four different horses, 
found that when watered before drinking, the consumption of water 
was irregular and was less than when they were watered during or 
after feeding, and that the corresponding digestibility was also less 
in nearly every case. Suggestive in this connection are the results of 
Foster and Lambert, 2 who found that in the dog a restricted supply of 
water tended to decrease the secretion of gastric juice. The fore- 
going results on animals seem to be in general accord with those of 
Hawk's extensive studies on the effects of water drinking in man. 



1 Jahresber. Agr. Chem., 28 (1899), 661. 



2 Expt. Sta. Rec, 25 (1911), 16. 



CHAPTER XVII 

THE PRODUCTION VALUES OF FEEDING STUFFS 

§ i. General Considerations 

735. Definition. — By the production values of feeding 
stuffs, as distinguished from the relative values discussed in 
the last chapter, is meant the actual effect produced by a unit 
weight of the substance in maintaining an animal or in sup- 
porting the processes of growth and fattening or of milk or work 
production. That such production values will also express 
relative values scarcely needs mention. 

Even at their best, comparisons based on the " digestible 
nutrients," such as have been in vogue for many years and 
have become familiar to all students of the subject, can show 
only the relative and not the absolute values of feeding stuffs. 
It is true that to the extent to which it may be assumed that 
the digestible nutrients as determined by analyses and digestion 
experiments actually consist of proteins, carbohydrates and 
fats, their amount may furnish a useful clue to the nutritive 
value of the material consumed. Even then, however, it affords 
no quantitative measure of the results to be expected, while in 
the case of most feeding stuffs, as appeared in Chapters II and 
III, the actual nature of the digested material has been but very 
incompletely investigated. Neither the chemistry of feeding 
stuffs nor the behavior of their various constituents in metab- 
olism is sufficiently well known to serve as the basis for any 
trustworthy estimate of their actual nutritive effect. The lat- 
ter can be determined only by a direct trial with the animal, 
and during the past two decades considerable progress has been 
made in this direction. 

736. Determination of production values. — By definition 
the production value is the effect produced upon the animal by 
a unit of the feed under consideration. The general methods 

630 



THE PRODUCTION VALUES OF FEEDING STUFFS 631 

for ascertaining this effect have been considered in Chap- 
ter VI. It was there shown that neither the gain nor loss of 
live weight or the gross weight of product is a sufficiently 
accurate measure of it (281-283, 604) and that the attain- 
ment of exact results requires the employment of some form 
of the balance experiment (285), based on the conception of 
the balance of nutrition. According to this conception, the 
production values of a feeding stuff for various purposes are 
measured, either by the extent to which it can prevent a 
loss of protein, ash and fat from the body during maintenance 
or work or can support the storage of these ingredients in the 
body or the milk. It was also pointed out in the same chapter 
that the investigations of the last thirty years have shown that 
the problem may be advantageously studied from the stand- 
point of energetics and that in this way the expression of the 
results may be notably simplified and unified. From this stand- 
point the feed is regarded as a supply of ash and protein (or 
amino acids) on the one hand and of energy on the other and 
its effect is similarly expressed by the gain or loss by the body 
of protein and ash and of chemical energy respectively. We 
may distinguish, therefore, between production values for pro- 
tein, for ash, and for energy. 

737. Two aspects of feed supply. — For a clear conception 
of the nature and significance of the production values of feed- 
ing stuffs, however, it is essential to distinguish between two 
aspects or functions of the feed supply. 

In the past the feed has been regarded chiefly as the source of 
the material necessary for the constructive processes going on 
in the body and of the energy required to support its metabolic 
activities. It supplies ash to maintain or increase the mineral 
matter of the body, protein (or amino acids) to build up its 
tissues or supply the protein of milk, energy to support the 
vital activities of the various organs. This aspect of the mat- 
ter has been the prominent one in the preceding chapters of 
this work. 

Recent investigation, however, is bringing into prominence 
another class of influences exerted by the feed upon the or- 
ganism. The studies upon the " vitamins," " accessory in- 
gredients," " growth substances," " stimulating substances," 
" specific effects of feeds," etc., which have been several times 



632 NUTRITION OF FARM ANIMALS 

referred to in Part III are rendering it increasingly evident that, 
quite aside from its value as a supply of structural material and 
of energy, the nature of the feed may profoundly influence 
the course and intensity of the metabolic processes. In par- 
ticular it appears that the absence of certain as yet ill-defined 
substances may constitute a limiting factor, particularly in 
growth, or may lead to the development of specific diseases, 
while, on the other hand, McCollum's observations on the ex- 
clusive use of wheat products (499) seem to indicate that similar 
effects of a more or less toxic character may follow the exces- 
sive consumption of feeding stuffs ordinarily regarded as health- 
ful. It is important, therefore, to secure as definite a concep- 
tion as possible of the significance of these new facts in their 
relation to the older conceptions of production values. 

738. Significance of "accessory ingredients." It is clear 
that the " accessory ingredients " (using this simply as a con- 
venient summary term for the various classes of substances 
indicated in the last paragraph) influence the nutritive value 
of a feeding stuff in an essentially different fashion than does 
the quantity of available ash, protein, and energy which it 
supplies. The latter limits the amount of production which the 
feeding stuff can support ; the presence or absence of the former 
may determine the extent to which this potential value is actu- 
ally realized. Thus in Chapter XI, experiments by Osborne and 
Mendel and by Hart and McCollum (498, 499) were described 
which show that a mixture of pure nutrients may be prepared 
which shall contain an abundant supply of complete, proteins, 
of ash and of energy but upon which young animals (rats) fail to 
grow, while the addition to such a mixture of minute amounts 
of substances associated with certain fats enables the rations to 
support normal growth. In some aspects of the matter, these 
" accessory ingredients " might be crudely compared with the 
lubricants of a machine, which of themselves furnish neither 
power nor material, but which enable power derived from the 
consumption of fuel to be more efficiently used and therefore 
conduce to the production of a larger output. 

A lack of lubricants in the case just supposed might conceiv- 
ably affect the output of a machine in one or both of two ways. 
The undue friction might slow down the machine as a whole 
so that less raw material would pass through it in a given time, 



THE PRODUCTION VALUES OF FEEDING STUFFS 633 

or it might affect specifically certain more delicate parts of the 
machine and so reduce the efficiency of the machine and cause it 
to yield less finished product per unit of raw material consumed. 
In which of these two ways a deficiency in " accessory sub- 
stances " affects the nutrition of an animal does not appear to 
have been determined. It would seem probable, however, that, 
in the case of a young animal, for example, a deficient dietary 
acts to slow down or stop the whole group of anabolic processes 
involved in growth. 1 The organs would thus be rendered in- 
capable of converting a normal daily amount of feed into body 
substances and a corresponding decrease in feed consumption 
would presumably follow. In such a case it is quite conceivable 
that such feed as was actually eaten in excess of the maintenance 
requirement might be just as efficient in producing gam and 
have as great a production value per unit as m a normal ration. 
In other words, it is conceivable that lack of the " accessory sub- 
stances " may, in a sense, affect the economic rather than the 
physiological efficiency of the ration. The writer has failed to 
.note any experiments in which this aspect of the matter has been 
considered. In practically all reported investigations upon the 
influence of " accessory substances," the feed consumption has 
been regulated by the appetite of the animal and in many in- 
stances has not even been reported. 

The undoubted importance of the accessory ingredients ot 
feeding stuffs has led, on the part of some writers, to a tendency 
which as yet appears hardly justified to minimize the signifi- 
cance of the production values in the older sense. The subject 
is too new and the field too broad to warrant dogmatic con- 
clusions, but it still remains true that the prime function of a 
feeding stuff is to supply structural material and energy for 
the body, and its potentialities in this respect are expressed in 
its production values. That the results attained by its use 
in practice are affected by other considerations has long been 
recognized. Thus, if a feeding stuff is unpalatable for some 
reason and is not eaten freely, the portion consumed may 
show a high nutritive effect per unit and yet the use of the 
feed be inadvisable. The presence of toxic substances might 

1 Naturally such an effect might be brought about by a retardation of certain 
specific metabolisms upon which the whole growth process depended and the spe- 
cific metabolisms affected might differ in different cases. 



634 NUTRITION OF FARM ANIMALS 

prevent the use of a feed in sufficient amounts to be profitable 
and yet the nutritive effect of the feed within the limits of 
tolerance might be considerable. 

Production values, then, if determined by means of balance 
experiments made under normal conditions, are to be regarded 
as showing the potential values of feeding stuffs as sources of 
matter and energy, i.e., their worth as constituents of a ration 
which contains sufficient amounts of whatever " accessory in- 
gredients " are necessary to ensure the normal course of metab- 
olism. The study of " accessory substances " in the broadest 
sense of the term has revealed an additional and apparently very 
important group of factors influencing the extent to which the 
potentialities of feeding stuffs are actually utilized. It is pos- 
sible that in the future there must be added to the require- 
ments already outlined for ash, protein (or amino acids) and 
energy for the various purposes of feeding, the requirements for 
the " accessory substances " necessary to secure the most 
efficient functioning of the cells and organs of the body. 

§ 2. Production Values as Regards Energy — Net 
Energy Values 

739. Recapitulation. — The consideration of the processes of 
nutrition in Part II, and in particular the study of metabolism 
and of the balance of nutrition in Chapters V and VI, has 
shown that the animal body is primarily a transformer of 
chemical energy and that quantitatively the most important 
function of the feed is to supply this energy. In the several 
chapters of Part III the conception of net energy values was 
developed and the requirements for net energy by different 
species of farm animals and for different purposes were dis- 
cussed. It is apparent from those discussions that the net 
energy value is only another name for the production value of 
a feeding stuff as regards energy as defined in the preceding 
section. It appears desirable at this point, therefore, to re- 
capitulate the general facts regarding the energetics of the 
animal body which are contained in previous chapters, and 
to consider in greater detail their bearing upon the production 
values of feeding stuffs, even at the expense of a certain amount 
of repetition. 



THE PRODUCTION VALUES OF FEEDING STUFFS 635 

740. Gross energy. — The energy supply of an animal is 
contained in its feed as chemical energy, and the maximum 
amount which any substance can furnish for the vital activities 
by its oxidation in the body is measured by its heat of com- 
bustion. This has been called its gross energy (315) to avoid 
the implication that it represents the total amount of energy 
associated with the substance. 

741. Losses of energy. — It rarely, if ever, happens, how- 
ever, that this maximum effect is realized. In practically every 
case a larger or smaller proportion of the chemical energy of 
the feed escapes unutilized. These losses of energy are of two 
general classes. 

First, a portion of the chemical energy of the feed fails to be 
transformed at all, leaving the body as chemical energy in the 
visible excreta and in the combustible gases arising from gastric 
and intestinal fermentations. 

Second, another portion of the chemical energy of the feed is 
indeed transformed, but at ordinary temperatures virtually re- 
sults merely in a superfluous heat production. It is true that 
the metabolism consequent upon feed consumption is not only 
unavoidable but may be regarded as a necessary expenditure of 
energy for the support of the activities connected with digestion 
and assimilation. Nevertheless, from the standpoint of the 
net gain or loss by the organism this portion of the feed energy, 
which ultimately takes the form of heat and escapes from the 
body, must be regarded as a loss. 

The losses of chemical energy 

742. Losses in feces. — Chemical energy escapes in the feces 
both in the undigested feed residues which they contain and 
in the excretory products which they carry. While the latter 
portion is not derived immediately from the feed consumed, 
but constitutes a loss of incompletely katabolized matter, it 
must, none the less, be included in estimating the net effect 
of a ration on the energy balance of the body. 

With herbivorous animals, the excretion in the feces con- 
stitutes the greatest loss of chemical energy, and the one which 
varies most as between different feeding stuffs or different species 
of animals, as is apparent from the results recorded in Table 187 



636 NUTRITION OF FARM ANIMALS 

(749). This is especially true of the energy of roughages, which 
contain much indigestible matter, but even with the more di- 
gestible materials the loss through the feces is relatively con- 
siderable. With swine it is relatively less than with herbivora 
because the former animals are usually largely fed on concen- 
trates. The influence of various conditions upon the losses in 
the feces, i.e., upon digestibility, has already been discussed in 
§ 3 of the previous chapter. 

743. Losses in urine. — The urine is especially the vehicle 
for the removal from the body of the end products of protein 
katabolism, of which urea is the most familiar and frequently 
the most abundant. Numerous other nitrogenous substances, 
however, are contained in the urine, particularly the purins and, 
in herbivorous animals, hippuric acid. Moreover, as stated 
in Chapter V (224, 225), the urine of herbivora in particular 
may contain relatively considerable quantities of non-nitrog- 
enous excretory products regarding the nature of which little 
is known. All these substances carry off a portion of the gross 
energy of the feed as unused chemical energy, the amount of 
the loss being measured by their heats of combustion. That 
the extent of these losses cannot be satisfactorily computed from 
the nitrogen content of the urine has already been pointed out. 

The loss of chemical energy in the urine, as appears from 
Table 187, constitutes a relatively small percentage of the 
total loss. As would be expected, it is quite variable, being 
higher as the feed supply is richer in protein, and lower with 
relatively indigestible substances where the loss in the feces is 
larger. 

744. Fermentation losses. — The gaseous products, chiefly 
methane, of the fermentation of the carbohydrates in the di- 
gestive tract of herbivora, especially of ruminants, carry off con- 
siderable amounts of unused chemical energy, one gram of 
methane, for example, having a heat of combustion of 13.344 
Calories. 

The extent to which the carbohydrates are attacked by the 
methane fermentation appears to be somewhat variable. 
Armsby and Fries l have observed that with cattle it is dis- 
tinctly greater on light than on medium or heavy rations and 
the same authors likewise observed a single instance of indi- 

1 Jour. Agr'l Research, 3 (1915), 445. 



THE PRODUCTION VALUES OF FEEDING STUFFS 637 

viAud difference in this respect between animals Recently 
Zuntz and Ms associates » have reported striking instances in 
whkh the extent of the methane fermentation m particular 
Tasteen markedly affected by the make-up of the rations and 
especially by the order in which the feeds were consumed, while 
V61U and his associates « have laid much stress upon the prac- 
tical importance of these results. No such marked differences 
were observed in Armsby and Fries' experiments but the range 
Tf eedhig stuffs used was not so wide. It is perhaps too ear y 
to udge of the full significance of Zuntz's results, but they should 
It C serve to correct the notion, ™?^!%£™* 
held by not a few, of digestion as a perfectly definite process 
and of a digestion coefficient as a sort of chemma constant. 
On the other hand, however, it seems quite possib e to over- 
Simate the effect of such variations in the digestive process 
Joule net energy values of feeding stuffs. On the whole 
they appear to be of far less significance than other factors to 

%rpSc e entage r of the gross energy which is lost in the fer- 
„JntL gases', as appears from Table 188 (749) »£«£ 
verv large It is naturally greatest in the case of feeding stutts 
^iSri-l^te^espeda^toea-ly^ble^^^ 
745 Computation of fermentation losses. - While the ex 
neimental determination of the energy losses in feces and 
S, comparatively easy task, requiring relatively simple 
annhances the determination of the fermentation losses neces- 
sfta teTthe use of the somewhat complicated and costly res- 
piratTon apparatus. In the absence of such an apparatus, how 
ever it is possible to compute the fermentation losses with a fair 
degr'e of accuracy from the results of the ordinary digestion 
experiment The methane fermentation attacks chiefly or 
Xly the carbohydrates (135, 140) and in the case of cattle in 
particular, it has been shown that the amount of methane pro- 
duced is in general proportional to the amount of total car 
Shydrates fcrude fiber and nitrogen-free extract digest d 

Kellner 3 in forty-four experiments with cattle on mixed 
rations found the average methane excretion to be 4.2 grams 

.Landw. Jahrb., 44 (1913), 765 ; Landw. Vers. Stat., 7SHS0 (.»), 78.. 
* Landw. Jahrb., 44 (1913). 68 S ; 45 (1913), 3*5- 
s Landw. Vers. Stat., S3 (1900), 415- 



638 NUTRITION OF FARM ANIMALS 

for each 100 grams of total carbohydrates digested, and the 
estimated results for ruminants recorded in Table 188 for the 
losses in methane were computed on that basis. With the 
addition of later unpublished experiments, Kellner's l aver- 
age was increased to 4.3 grams. Later experiments by Armsby 
and Fries 2 have given slightly higher averages, viz., 4.8 grams 
for roughages and 4.7 grams for concentrates. No similar re- 
sults for the smaller ruminants have been reported but probably 
it may be safely assumed that the average for cattle is substan- 
tially applicable to these species also. 

In the horse the principal seat of the methane fermentation 
is the colon and ccecum (128). Since the more soluble carbo- 
hydrates of the feed are largely or entirely digested before reach- 
ing these organs, methane is much less copiously produced 
than in the case of ruminants and may be regarded as derived 
chiefly from the fermentation of crude fiber. 

In respiration experiments on mixed rations of oats, hay 
and straw, Lehmann, Zuntz and Hagemann 3 observed as 
the result of eight rather discordant experiments an average 
total excretion of methane of 4.73 grams per 100 grams di- 
gested crude fiber and in addition an average excretion of 0.203 
gram of hydrogen per 100 grams digested crude fiber. In 
more recent experiments, Von der Heide, Steuber and Zuntz, 4 
using a Regnault-Reiset respiration apparatus (298), obtained 
for the methane excretion per 100 grams digested crude fiber 
9.06 grams on hay and 2.28 grams on straw pulp. Using 
the average of these rather discordant experiments, the fer- 
mentation losses in the case of the horse may be approximately 
computed from the amount of crude fiber digested. 

Swine with their simpler alimentary canal suffer but small 
losses from fermentation in the digestive tract. 

Fingerling, Kohler and Reinhardt 5 found the amounts of 
combustible gases excreted too small to be determined with 
their form of Pettenkofer apparatus. Von der Heide and 
Klein 6 in three experiments with a Regnault-Reiset apparatus 
obtained the following results : — 

1 Ernahrung landw. Nutztiere, 6th Ed., p. 94. 

2 Jour. Agr'l Research, 3 (1915), p. 450. 3 Landw. Jahrb., 23 (1894), 125. 

4 Biochem. Ztschr., 73 (1916), 161. 5 Landw. Vers. Stat., 84 (1914), 197- 

6 Biochem. Ztschr., 55 (1913), 195. 



THE PRODUCTION VALUES OF FEEDING STUFFS 639 

Table 185. — Excreted by Swine per 100 Grams Digested 
Carbohydrates 



Period I 
Period II 
Period III 

Average 



Hydrogen 
Grams 




Although there is considerable range in the results of in- 
dividual experiments, and while those on non-ruminants are 
few in number, nevertheless, the foregoing figures afford a basis 
for an approximate estimate of the losses of chemical energy 
in the combustible gases. Summarizing the available data 
and computing the equivalent quantities of energy, it appears 
that the following average deductions may be made from the 
gross energy of the feed for the fermentation losses. 

Table 186. — Factors for Computing Fermentation Losses 



Per 100 grams digested carbohydrates 
Ruminants — Methane 

Swine — Methane 

Hydrogen 

Total 

Per 100 grams digested crude fiber 

Horse — Methane 

Hydrogen 

Total 



4-9 



Weight 


Equiva- 
lent 
Energy 


Grams 


Cals. 


4-5 


60.1 


O.65 


8.7 


0.07 


2.4 


O.72 


II. I 


4-7 


62.7 


0.2 


7.0 



69.7 



Metabolizable energy 

746. Definition. — The difference between the chemical 
energy of the feed and that lost in the excreta shows how much 
of the former is capable of being converted into other forms in 
the body, either during the changes which the feed undergoes in 



640 



NUTRITION OF FARM ANIMALS 



the digestive tract or in the course of metabolism in the tissues. 
As stated in Chapter VI (323), this convertible portion of the 
feed energy has been given various names by different investi- 
gators, such as "physiological heat value," " fuel value," " avail- 
able energy," etc., but following a suggestion made earlier by 
the writer it is here designated as " metabolizable energy." 

747. Method of determining. — As is apparent from the 
foregoing paragraphs, the direct determination of the metab- 
olizable energy of a feeding stuff or ration requires the meas- 
urement of the amounts and heats of combustion of the feed 
and of the solid, liquid and gaseous excreta by the methods 
outlined in Chapter VI. These quantities being known, a 
simple subtraction gives the metabolizable energy. Thus the 
results of the experiment used as an illustration in Chapter VI 
(322), put in a somewhat more detailed form, were as follows : — 

Table 187. — Example of Determination of Metabolizable Energy 



Daily feed 
Timothy hay . . . 
Linseed meal . . . 

Daily excreta 

Feces 

Urine 

Methane 

Metabolizable energy 
By difference . . . 



Fresh 
Weight 


Dry 

Matter 


Grams 


Grams 


6,988 


6,086 


400 


354 


16,619 


2,948 


4,357 


— 


142 


142 


— 


— 



Heat of 

Combustion 

or Dry 

Matter per 

Gram 



Cals. 

4,556 
5,iii 

4,831 
0,23c 1 

13,344 



Energy 
of Feed 



Cals. 

27,727 
1,811 



29,538 



Energy 

of 
Excreta 



Cals. 



14,243 
1,210 
1,896 



12,189 
29,538 



748. Correction for gain or loss of protein. — In the foregoing 
experiment the animal gained 15.2 grams of fat and 66.6 grams of 
protein and therefore stored up in its body equivalent amounts of 
energy, viz., 

In protein, 5.7 Cals. X 66.6 = 380 Cals. 
In fat, 9.5 Cals. X 15.2 = 144 Cals. 
1 Per gram fresh urine. 



THE PRODUCTION VALUES OF FEEDING STUFFS 641 

The 144 Cals. of energy contained in the fat, however, although 
not actually transformed into other forms of energy, were capable of 
such transformation had the demands of the organism required it, 
and therefore constitute part of the metabolizable energy of the feed. 
With the 380 Cals. contained in the protein stored up, however, the 
case is different. Had these 66.6 grams been katabolized, part of 
their energy would have escaped in the resulting nitrogeneous meta- 
bolic products. According to Rubner each gram of urinary nitrogen 
derived from lean meat is equivalent to 745 Cals. of chemical energy. 
The katabolism of the 66.6 grams of protein, therefore, would have in- 
creased the chemical energy of the urine by 83 Cals, while only 297 
Cals. would have been transformed. This amount of 83 Cals. must 
consequently be added as a correction to the urinary energy as measured 
in computing the metabolizable energy. In case of a loss of protein 
from the body a similar correction must evidently be subtracted. 

When a respiration apparatus for the determination of the 
combustible gases is not available, their amount may be esti- 
mated from the digestible carbohydrates in the manner al- 
ready outlined (745), so that it is possible to estimate the metab- 
olizable energy with a considerable degree of accuracy from the 
results of an ordinary digestion experiment to which has been 
added the collection of the urine and determinations of the heats 
of combustion of the visible excreta. The additional labor 
thus required is so small that it is to be hoped that in future 
digestion experiments it may be undertaken whenever possible 
and that in this way more extensive data may be secured re- 
garding the metabolizable energy of feeding stuffs. While 
such results do not show the production values of the rations 
(750), they constitute an important step toward their more 
exact determination. 

749. Experimental Results. — There are on record a some- 
what limited number of experiments with cattle and a few 
with swine in which the losses of energy in the feces, urine and 
methane respectively have been determined directly, while in 
a considerably larger number the losses of methane have been 
estimated from the digestible carbohydrates (crude fiber plus 
nitrogen-free extract) in the manner just described. The re- 
sults of these experiments are recorded in Table 188, 1 which 
shows the percentages of the gross energy which were carried 
1 This table is not claimed to be an exhaustive compilation of data, but is be- 
lieved to be fairly complete. 



2 T 



642 



NUTRITION OF FARM ANIMALS 



off in the several excreta and, by difference, the percentages 
which were metabolizable. The metabolizable energy per 
gram of digestible organic matter is also added, since, as will 
appear subsequently, it forms a convenient basis for the com- 
putation of metabolizable energy when direct determinations 
of it are not available. 

Table 188. — Apparent Metabolizable Energy 



Cattle 
Roughages 

Meadow hay 

Meadow hay 

Timothy hay 

Red clover hay .... 
Mixed timothy and red 

clover hay 

Alfalfa hay 

Hay from irrigated meadows 

Ensiled hay 

Oat straw 

Wheat straw 

Straw pulp 

Maize stover 

Average 

Concentrates 

Maize meal 

Wheat bran 

Hominy chop 

Mixed grains No. i . . . 
Mixed grains No. 2 . . . 

Millet 

Palmnut meal 

Distillers' slop (from 

potatoes) 

Beet molasses 

Beet molasses 

Distillers' residue from 

grapes + beet molasses . 

Pumpkins 

Starch 

Wheat gluten 

Average 



Author 



Kellner 
Tangl, et al. 
Armsby and Fries 
Armsby and Fries 

Armsby and Fries 
Armsby and Fries 
Tangl, et al. 
Tangl, et al. 
Kellner 
Kellner 
Kellner 
Armsby and Fries 



Armsby and Fries 
Armsby and Fries 
Armsby and Fries 
Armsby and Fries 
Armsby and Fries 
Tangl, et al. 
Voltz, et al. 

Voltz, et al. 
Voltz, et al. 
Kellner 

Tangl, et al. 
Tangl, et al. 
Kellner 
Kellner 



Percentage Losses 


< 

H 

w 

W PQ 
O < 
■< N 

53 5 

w 



« 

w 

PL, 








In 
Feces 


In Urine 


In 

Meth- 
ane 


% 


% 


% 


% 


40.96 


5-7i 


6.77 


46.56 


44.6 


5-5 


6.81 


43-1 


46.4 


3-8 


7-3 


42-S 


41.9 


6.8 


6-5 


44-8 


43-9 


5-2 


7-4 


43-5 


44.1 


5-8 


6.2 


43-9 


47-5 


3-o 


6.6 1 


42.9 


62.5 


o. 4 (?) 


4.9 1 


32.2 


56.8 


2.1 


5-3 


35-8 


58.2 


2.4 


8.3 


3I-I 


12.8 


-0.8 


12.5 


75-5 


42.8 


4.2 


7-9 


45-1 


13-3 


5-i 


10.0 


71.6 


31.8 


5-4 


7-4 


55-4 


12.2 


3-8 


9.2 


74-8 


19.2 


7.2 


8.2 


65-4 


22.7 


4.4 


8.1 


64.8 


34-6 


3-4 


7-7 1 


54-3 


19-3 


— 2.0 2 


6.9 1 


75-8 


61. 1 


4-5 2 


5-4 1 


29.0 


-46.5 


— 3.0 2 


I3-7 1 


135.8 


9-9 


2.9 


"•3 


75-9 


59-i 


3-4 


3-8> 


33-7 


20.1 


2.8 


6.9 1 


70.2 


17.6 


-0.7 


9.2 


73-9 


20.2 


131 


0.1 


66.6 



3a 
a s 

H < 

So 
« < 

o 



Cals. 



3-5oi 
3-437 
3.487 
3.486 

3-390 
3-605 
3.600 
3.698 
3-740 
3-3IO 
3-640 
3-45Q 
3-529 

3-797 
3-954 
4-075 
3-9io 
3-879 
3-787 
4.849 

2.703 
536i 
3-473 

4.519 
4.287 
3-603 
4-792 
4.078 



1 Estimated. 



2 Not corrected to N. equilibrium. 



THE PRODUCTION VALUES OF FEEDING STUFFS 643 



Table ii 



Apparent Metabolizable Energy (Continued) 



Author 



Sheep 
Roughages 
Meadow hay .... 
Meadow hay .... 
Hay from peat meadows 
Hay from alkali soil . . 
Hay from same, irrigated 
Alpine hay 

Average 

Alfalfa hay 

Average 



Dried potato vines . . . 
Same with fruit .... 
Hay and dried potato vines 
Hay and ensiled potato 

vines 

Wheat straw 



Average 

Concentrates 

Oats 

Millet 

Corn-and-cob meal . . . 

Palmnut meal 

Lentils 

Distillery slop from pota- 
toes 

Beet molasses .... 

Average 



Horses 
Roughages 
Meadow hay .... 
Hay from peat meadow 
Hay from alkali soil . . 
Hay from same, irrigated 

Alpine hay 

Sour meadow hay . . 

Silage from same . . . 

Average 



TangI, el al. 
Voltz, el al. 
Tangl, el al. 
Tangl, el al. 
Tangl, el al. 
Tangl, et al. 

Tangl, et al. 

Voltz, et al. 
Voltz, et al. 
Voltz, et al. 

Voltz, et al. 
Voltz, et al. 



Tangl, et al. 
Tangl, el al. 
Tangl, et al. 
Voltz, et al. 
Voltz, et al. 

Voltz, et al. 
Voltz, et al. 



Tangl, et al. 
Tangl, el al. 
Tangl, et al. 
Tangl, et al. 
Tangl, et al. 
Tangl, et al. 
Tangl, et al. 



Concentrates 

Oats 

Distillery residue from 
grapes and beet molasses 

Average 



Tangl, et al. 
Tangl, et al. 




23-2 
18.6 



55-1 
66.1 
59-3 
50.4 
50.1 
66.4 
70.0 



41.4 
66.9 



19 



1 
0.8 1 
1.6 1 

2.0 1 

1.6 1 

1.5 » 

1.6 1 



3.7 0.2 1 

0.8 1 



39-4 

29.4 

45-4 

43- 

44.6 

28.4 

24.7 



54-7 
30.9 



3-707 
3-854 
3-803 
3-741 
3.915 
3.607 
3-352 
3-712 



4-493 

4-76i 
4.627 



1 Estimated. 



2 Not corrected to N. equilibrium. 



644 NUTRITION OF FARM ANIMALS 

Table i 88 — Apparent Metabolizable Energy (Continued) 



Author 



Percentage Losses 



In 
Feces 



In 

Urine 



In 

Meth- 
ane 



w 

M hi 

w o 
u n 

W H 

P* w 



O 

, <** 

W W 

O u 

< 

o 



Horses 
Mixed Rations 
Oats, hay and straw 
Oats, hay and straw 
Oats, hay and straw 
Oats, hay and straw 
Oats, hay and straw 
Oats, hay and straw 

Average .... 

Swine 
Concentrates 

Millet 

Pumpkins 

Barley and a little flesh 
meal 

Flesh meal 

Wheat gluten 

Starch 

Straw pulp 

Sugar 

Peanut oil 

Barley, dried potatoes and 
dried yeast 

Same + palm oil . . . . 

Same + dried potatoes . 

Computed for oil ... 

Computed for dried pota- 
toes 

Whole milk 

Skim milk and saccharified 
starch 

Skim milk and raw starch . 

Skim milk and fat . . . 
Averages 

Flesh meal and wheat 

gluten 

Whole milk .... 
Peanut oil . . . . 
Other rations . . . 



Geese 



Maize 
Millet 

Millet 



% 



Zuntz 
Zuntz 
Zuntz 
Zuntz 
Zuntz 
Zuntz 



and Hagemann 
and Hagemann 
and Hagemann 
and Hagemann 
and Hagemann 
and Hagemann 



Tangl, et al. 
Tangl, et al. 

Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 

V. d. Heide and Klein 
V. d. Heide and Klein 
V. d. Heide and Klein 
V. d. Heide and Klein 

V. d. Heide and Klein 
Wellmann 

Wellmann 
Wellmann 
Wellmann 



4-7 

3-4 
3-8 
3-5 



% 



28.8 


3-4 


25.6 


3-9 


16.3 


3-3 


6.9 


8.9 


7-4 


10.9 


2.6 


— 2.0 


14.4 


- 1.8 


2.7 


0.4 


0.4 


- 0.5 



9.8 

11.3 
10.5 

7-5 



Ducks 



Tangl, et al. 
Tangl, et al. 

Tangl, et al. 



23-9 
43-8 



53-6 



% 


% 


0.2 1 

I.4 1 


67.2 
69.1 


— 


80.4 
84.2 
81.7 


— 


99-4 

87.4 

96.9 

100.9 


— 


85.5 


— 


85-3 
85.7 
89.0 


— 


76.1 
56.2 


— 


46.4 



% 

4-474 
3-236 
3-403 
3-803 
3.980 
5-Q52 

3-991 



4-335 
3-460 

4.521 
5.629 
4.908 
4.076 
3-952 
3-75o 
8-997 

4-237 
4.442 
4.160 
9-552 

4.111 
5-467 

4-519 
3-825 
5-994 



5. 269 

5-467 
8-997 
4-055 



3-753 
2.723 



2.323 



1 Estimated. 



THE PRODUCTION VALUES OF FEEDING STUFFS 645 

750. Significance of metabolizable energy. — By metab- 
olizable energy, as already explained, is meant simply the 
energy capable of transformation in the body, with no impli- 
cation as to the proportion of the energy thus transformed 
which can be utilized by the organism. The heat evolved 
during the methane fermentation, for example, constitutes part 
of the metabolizable energy as thus defined, although it does 
not enter into the tissue metabolism. 

The metabolizable energy of a feeding stuff does not meas- 
ure its production value, since it takes account of only one of 
the two classes of losses to which its chemical energy is sub- 
ject. Obviously, however, it is an essential factor in fixing 
that value, since frequently from one-fourth to one-half or more 
of the feed energy is thus rejected unused. The determination 
or estimation of the metabolizable energy of a feeding stuff is, 
therefore, an important step in ascertaining its production 
value as regards energy, and constitutes an advance over the 
simple determination of digestibility, since it takes account of 
the losses in urine and methane as well as of those in the feces. 

751. Real and apparent metabolizable energy. — The metab- 
olizable energy of a feeding stuff as determined experimentally 
in the manner illustrated in a preceding paragraph (747) is the 
aggregate effect as regards energy of all the influences which the 
feeding stuff exerts on the digestive processes. 

For example, in one of Kellner's experiments beet molasses 
added to a basal ration diminished the amount of energy car- 
ried off in the methane by 135.8 Cals., while at the same time 
it so depressed the digestibility of the basal ration that the 
amounts lost in the feces and urine were increased by 1865.9 
Cals. and 272.3 Cals. respectively. By the method of com- 
putation here used, the algebraic sum of these amounts is vir- 
tually regarded as representing the losses of energy from the 
molasses and is subtracted from the gross energy of the latter 
to obtain its metabolizable energy. The metabolizable energy 
as thus computed expresses the net increase in the amount of 
energy available for conversion in the body and may be called 
the apparent metabolizable energy. 

On the other hand, the results for the metabolizable energy 
of the digestible nutrients recorded in the next paragraph in- 
clude corrections for these secondary effects. They aim to show 



646 NUTRITION OF FARM ANIMALS 

the actual amounts of metabolizable energy supplied by the 
digested portions of the feed irrespective of its secondary effects 
— i.e., to express its real metabolizable energy. Such figures 
give a more accurate idea of the store of metabolizable energy 
contained in the feeding stuff regarded by itself, while the ap- 
parent metabolizable energy is better adapted for use in a dis- 
cussion of questions of feeding. 1 The distinction is similar to 
that already discussed in Chapter III (167) between real and 
apparent digestibility. 

752. Computation of metabolizable energy from digestible 
nutrients. — While, in the absence of a respiration apparatus, 
the metabolizable energy of a feeding stuff or ration may be 
estimated with a fair degree of accuracy by the method out- 
lined in previous paragraphs, not every experimenter is equipped 
to determine the heats of combustion of the feed and the visible 
excreta, and no satisfactory method of computing them is avail- 
able. Various attempts have accordingly been made to compute 
the metabolizable energy of feeding stuffs from chemical data. 

One such method is that employed by Rubner and by At- 
water for estimating the metabolizable energy of the food of 
man and of carnivora as described in Chapter VI (324), their 
factors for protein, carbohydrates and fat being applied directly 
to the digestible nutrients of feeding stuffs, and several tables 
of energy values as thus computed have been published. Later 
investigations, however, showed that the results thus obtained 
were much too high in the case of herbivorous animals, es- 
pecially of ruminants. To cite but a single instance, experi- 
ments on cattle by the writer 2 gave the results shown in Table 
189 for metabolizable energy as compared with those computed 
by the use of Rubner's factors, and Kellner's somewhat earlier 
results 3 led to the same general conclusion. 

There are two principal reasons for this discrepancy. The 
first is the extensive fermentation of the carbohydrates in the 
digestive tract of ruminants, leading to a relatively larger loss 
of energy in the combustible gases excreted. The second rea- 
son is the fact that the urine of herbivora carries off much 
more non-nitrogenous material (224) than is the case with man 
or carnivora. The results of direct determinations on swine 

1 Compare Armsby, Principles of Animal Nutrition, pp. 291-293 and 333-335. 

2 Penna. Expt. Sta., Bui. 71, p. 7. 

3 Landw. Vers. Stat., 53 (1904), 440-449. 



THE PRODUCTION VALUES OF FEEDING STUFFS 647 

show much smaller differences between the observed and com- 
puted results, the fermentation losses in particular being notably 
less with swine than with cattle or sheep (745). 

Table 189. — Comparison of Metabolizable Energy per Pound 



Timothy hay 
Clover hay . 
Maize meal . 



Computed by 
Rubner's 
Factors 



Calories 

875 
901 

1525 



Directly 
Determined 



Calories 

777 

742 

1308 



Kellner has attempted to secure factors for cattle similar to 
those of Rubner for men and carnivora by means of experiments 
in which approximately pure nutrients (starch, sugar, oil, gluten) 
were added to a basal ration. In the case of starch, for ex- 
ample, the increase in the amount of nitrogen-free extract di- 
gested was compared with the increase in the total metaboliz- 
able energy of the ration, the losses of energy in feces, urine 
and methane being determined with the aid of a respiration ap- 
paratus by the method of indirect calorimetry (329). The re- 
sults are corrected for the effects of the starch upon the digest- 
ibility of the several nutrients of the basal ration and upon 
the losses from the latter in urine and methane, i.e., the real 
metabolizable energy is computed. A few similar determina- 
tions on other species have also been reported. 

In an earlier publication 1 the writer has discussed in con- 
siderable detail the recorded experiments regarding the metab- 
olizable energy of the nutrients digested by farm animals 
with the results summarized in the following table. To the 
extent to which satisfactory factors can be selected, this table 
may be used to compute the metabolizable energy of feeding 
stuffs or rations whose digestibility is known, but it should be 
noted that the results will include no allowance for the secondary 
effects of the feed on the digestive processes and will prob- 
ably be higher than the " apparent " metabolizable energy 
obtained by direct experiment. 

1 Principles of Animal Nutrition, pp. 302-335. 



648 



NUTRITION OF FARM ANIMALS 



Table 190. — Metabolizable Energy of Digestible Nutrients per 

Gram 



hay 



Protein (N X 6.25) : 

From wheat gluten . . . 

From wheat gluten (N X 5.7) 

From beet molasses . . 

From mixed grain . . . 

From mixed ration of oats, 
and straw 

From meadow hay . . . 

From timothy hay . . . 

From straw 

Fat: 

From peanut oil ... 

From hay (ether extract) 
Carbohydrates : 

Starch, Kellner's experiments . 

Starch, Kiihn's experiments 

Nitrogen-free extract (assumed) 

Crude fiber, of straw pulp . . 

Crude fiber, of hay fed alone . 

Crude fiber, of hay added to basal 
ration 

Crude fiber, of oat straw 

Crude fiber, of wheat straw 

Crude fiber, of mixed ration 



Cattle 



Cals. 
4.894 
4-958 
3-984 



1.272 
3-°57(?) 
(?) 



8.821 
8.322 

3-763 
3.648 

3.606 
3-3H 



3.606 

3-437 
3.001 



Horse 



Swine 



Cals. 



3.228 



4.185 



3-523 



Cals. 



4.083 



753. Computation of metabolizable energy from digestible 
organic matter. — A more simple and direct method of compu- 
tation may, however, be employed, based on the total digest- 
ible organic matter of the ration. As already pointed out, 
the differences shown in Table 188 between the percentages of 
the gross energy of different feeding stuffs which are metabo- 
lizable are due chiefly to differences in the proportion of the 
chemical energy carried off in the feces, while the losses in urine 
and methane are far more uniform. Accordingly, the metabo- 
lizable energy per unit of digestible organic matter necessarily 
exhibits much smaller variations than that per unit of dry 
matter, and in fact shows a striking degree of uniformity. 
Selecting those averages which appear most trustworthy, the 
results may be summarized as follows : — 



THE PRODUCTION VALUES OF FEEDING STUFFS 649 

Table 191. — Metabolizable Energy per Kilogram Digestible Or- 
ganic Matter 



Roughage 

Cattle 

Sheep 

Horse 

Concentrates 

Cattle 

Sheep 

Horse 

Swine x 



Number 

of Single 

Trials 


Maximum 


Minimum 




Therms 


Therms 


73 


3-74 


3-31 


33 


3-77 


3-29 


13 


3-92 


3-35 


3i 


4-85 


3-79 


25 


4.08 


3-41 


8 


4.76 


4.49 


36 


5.63 


3-46 



Mean 



Therms 
3-53 

3-56 

3-7i 



4.04 

3.85 
4.62 
4.40 



A similar degree of uniformity appears when the results on 
mixed rations are compared, as the following summary shows : — 

Table 192. — Metabolizable Energy per Kilogram Digestible 
Organic Matter in Mixed Rations 



Cattle 

Kellner and Kdhler . . . 
Armsby and Fries . . . . 

Voltz, et al , 

Tangl, et al 

All experiments . . . . 

Sheep 

Tangl, et al 

Voltz, et al 

All experiments .... 

Horse 

Lehmann, Zuntz and Hage 

mann 

Tangl, et al 

All experiments .... 



Number 

of Single 

Trials 



38 
26 

4 
_8 

76 

16 
19 
35 



14 



Maximum 



Therms 

3-72 

3-89 
4.12 

4-H 

4.12 



4-30 
4-Q5 

4-30 



4-47 
4-3i 

4-43 



Minimum 



Therms 

3-48 
3-5i 
3-76 
3-°4 
3-48 



3-5° 
3-i5 
3-i5 



3-24 
4-19 
3-48 



Mean 



Therms 

3.60 

3-73 
3-98 
3^5 

3-67 



3-79 
3-79 

3-79 



3-99 
4-25 
4.06 



1 Excluding feeds containing much oil. 



650 



NUTRITION OF FARM ANIMALS 



Feeding stuffs, rich in protein and fat, especially the latter, 
naturally give higher values, as is illustrated by the following 
results, likewise taken from Table 188. 

Table 193. — Metabolizable Energy per Kilogram Digestible 

Organic Matter 
Palmnut meal 

Cattle 4.85 Therms 

Sheep 3.98 Therms 

Wheat gluten 

Cattle 4.79 Therms 

Flesh meal 

Swine 5.63 Therms 

Taking the pound as the unit for reasons of practical con- 
venience, it is believed that for the approximate computation 
of the metabolizable energy of ordinary feeding stuffs or ra- 
tions whose content of digestible organic matter is known or 
can be estimated, the following factors may be used, at least for 
ruminants, without serious error : — 

Table 194. — Metabolizable Energy per Pound Digestible Or- 
ganic Matter 



Roughage 

Mixed rations — roughage and concentrates 

Concentrates 

Grains and similar material 

With less than 5 per cent digestible fat . 

With more than 5 per cent digestible fat . 
Oil meals and materials high in protein 



Ruminants 


Swine 


Therms 


Therms 


1.588 


— 


I.769 1 

1.814J 


1-935 


1. 996-2. 177 


2.390 



Horses 



Therms 

1.683 
1.810 



2.096 



Losses of energy in heat production 

It was stated in a previous paragraph (741) that the gross 
energy of a feeding stuff is subject to two classes of losses, viz., 
losses of untransformed chemical energy in the excreta and 
losses through conversion into heat. The losses of chemical 
energy have been discussed in the preceding paragraphs. The 
second class of losses has now to be considered. 



THE PRODUCTION VALUES OF FEEDING STUFFS 651 

754. Influence of feed consumption on metabolism. — As 

is evident from § 1 of Chapter VIII (365), the fact that the 
consumption of feed tends to increase the heat production of an 
animal has become a commonplace of physiology. The mag- 
nitude of the effect varies within rather wide limits according 
to the species of animal and the chemical and physical proper- 
ties of the feed, while there is still more or less difference of 
opinion as to its causes. Zuntz and his associates have called 
it " work of digestion " and have attributed it largely to in- 
creased muscular and glandular activity of the digestive and 
excretory organs. Numerous investigations in this field have 
been made on carnivora or on man, in which the increase of 
the metabolism is not usually very large except when much pro- 
tein is consumed. The more recent experiments on these species 
appear to have shown that the mechanical work of the digestive 
organs is but a small factor and that the term " work of di- 
gestion " is not a fortunate one. With herbivora and especially 
with ruminants, on the other hand, the total effect on the heat 
production is quantitatively much more marked, and the 
mechanical factor is of greater significance. 

755. Results on cattle. — As illustrated in an earlier chapter 
(364, 449) the effect of feed consumption upon the metabolism 
of ruminants may be determined by comparing two periods in 
which different amounts of the same feeding stuff or ration are 
consumed, the increment of heat production on the heavier 
ration being compared with the additional amount of feed con- 
sumed. The experiments thus far reported have been almost 
exclusively upon cattle, the principal ones being the pioneer 
investigations of Kellner and Kohler l and the later ones of 
Armsby and Fries. 2 

Most of Kellner and Kohler's experiments were made on super- 
maintenance rations. The heat production was not measured directly, 
but computed from the balance of carbon and nitrogen in the 
manner indicated in Chapter VI (329), i.e., by indirect calorimetry. 
Only a few of their results have as yet been published in full, but 
from data regarding a few of the other experiments contained in 
Kellner's book, the increments of heat production may be computed. 

1 Landw. Vers. Stat., 47 (1896), 275; 50 (1898), 245; 53 (1900), 1-474. Die 
Ernahrung der landwirtschaftlichen Nutztiere, 6th Ed., Berlin, 191 2. 

2 Jour. Agr. Research, 3 (1915), 435. 



652 



NUTRITION OF FARM ANIMALS 



Armsby and Fries' experiments included both submaintenance and 
supermaintenance rations and the heat was measured directly with a 
respiration calorimeter. 

As elsewhere summarized by the writer, the average results 
derived from the two series of experiments are as follows : — 

Table 195. — Increment of Heat Production by Cattle 





Heat Incre- 


Experi- 


ment PER IOO 


menters * 


lb. Dry 




Matter Eaten 




Therms 


A&F 


35-47 


A&F 


44-13 


K&K 


42.27 


A&F 


44-45 


A&F 


53-03 


K&K 


47.40 


K&K 


56.88 


K&K 


43-46 


A&F 


48.31 


K&K 


39-78 


K&K 


46.00 


K&K 


51.62 


K&K 


52.62 


A&F 


58.33 


A&F 


61.92 


A&F 


53-39 


A&F 


60.19 


A&F 


5I-76 


K&K 


44.36 


K&K 


54-79 


K&K 


45-68 


K&K 


52-57 


K&K 


44.82 


K&K 


56.61 


K&K 


78.34 


K&K 


95.08 



Roughage 

Timothy hay 

Red clover hay 

Red clover hay 

Mixed hay 

Alfalfa hay 

"Grass hay" 

Meadow hay 

Rowen 

Maize stover 

Barley straw 

Oat straw 

Wheat straw 

Straw pulp 

Concentrates 

Maize meal 

Hominy feed 

Wheat bran 

Grain mixture No. 1 2 . 
Grain mixture No. 2 3 . : . 
Cottonseed meal .... 

Linseed meal 

Palmnut meal 

Peanut meal 

Beet molasses 

Starch 

Peanut oil 

Wheat gluten 



1 In this and following tables, A&F signifies Armsby and Fries and K&K 
Kellner and Kohler. 

2 Wheat bran, 14.28 per cent; corn meal, 42.86 per cent; old process linseed 
meal, 42.86 per cent. 

3 Corn meal, 60 per cent ; crushed oats, 30 per cent ; old process linseed meal, 
10 per cent. 



THE PRODUCTION VALUES OF FEEDING STUFFS 653 

756. Results on sheep. — In a series of respiration experi- 
ments upon two sheep by Kern and Wattenberg, reported by 
Henneberg and Pfeiffer, 1 varying amounts of nearly pure pro- 
tein in the form of conglutin or of flesh meal were added to a 
basal ration of hay and barley meal. The writer 2 has com- 
puted from the recorded results of these experiments the metab- 
olizable energy of the additions to the basal ration and the 
energy of the resulting gain. The difference between the two 
shows the amount of energy lost as heat. 

Table 196. — Increment of Heat Production by Sheep 





Period 


Dry 

Matter 

of 
Added 
Feed 


Metabo- 

LIZABLE 

Energy 

or 
Added 
Feed 


Energy 
or Re- 
sulting 
Gain 


Heat Increment 




Total 


Per 100 

Lb. Dry 

Matter 

Eaten 






Grams 


Cals. 


Cals. 


Cals. 


Therms 


f 


II 


117. 6 


S88.4 


517.8 


70.6 


27.24 


Conglutin . . , \ 


III 


234.8 


1 100.3 


741.8 


358.5 


69.26 


[ 


IV 


350.8 


1639.2 


1 106.9 


532.4 


68.86 


Flesh-meal . . . < 


V 


258.0 


1131.7 


672.5 


459-2 


69.31 


VI 


03-5 


454-9 


3I5.7 


139.2 


49.71 



The results are notably lower than those obtained by Kellner 
for wheat gluten fed to cattle, although in the three middle 
periods they are higher than those found with that species for 
other concentrates, but there are several points of uncertainty 
in the experimental results and the method of computation is 
an approximate one. On the whole, pending further investi- 
gation, it appears probable that the results obtained with cattle 
may, without very serious error, be regarded as applicable to 
other species of ruminants. 

757. Results on swine. — The data regarding the increment 
of heat production consequent on the consumption of feed by 
swine, although more abundant than those for sheep, are still 
rather meager. Respiration experiments made by Meissl, 
Strohmer and Lorenz 3 in a study of the sources of animal fat, 

1 Jour. Landw., 38 (1890), 215. 2 Principles of Animal Nutrition, pp. 463-465. 
3 Ztschr. Biol., 22 (1886), 63. 



654 NUTRITION OF FARM ANIMALS 

and by Kornauth and Arche * upon the nutritive value of 
cockle may be made the basis of estimates of the energy expendi- 
ture due to feed consumption, while the later investigations 
of Von der Heide and Klein, 2 of Fingerling, Kohler and Rein- 
hardt 3 and of Wellmann, 4 were directed more specifically 
toward a study of the energy relations. 

Neither of the two investigations first mentioned included any 
energy determinations, but by substantially the same method as that 
applied in the previous paragraph to experiments with sheep, assum- 
ing an average maintenance requirement, the heat increment per 
unit of feed may be computed. 

Von der Heide and Klein, in Zuntz's laboratory, have measured with 
the aid of a respiration apparatus of the Regnault-Reiset type (298) 
the metabolism of three swine on a basal ration slightly more than 
sufficient for maintenance and consisting of barley meal, dried potatoes 
and dried yeast, and also the effect of the addition to this basal ration 
of dried potatoes and of palm oil. The energy of the feed and excreta 
was determined. Estimating the fasting katabolism of the three ani- 
mals from the body surface, the results may be computed as in the 
two previous experiments. A computation from the total heat in- 
crements above the basal ration (i.e., without correction for the dif- 
ferences in live weight) gives somewhat higher results. 

Fingerling, Kohler and Reinhardt, in experiments on two growing 
swine about eight months old, added approximately pure nutrients 
(starch, peanut oil, straw pulp, wheat gluten, flesh meal and sugar) 
to a basal ration consisting of ground barley with a little flesh meal. 
The animals gained steadily in weight. By a comparison of the first 
and last periods, on the basal ration, the authors compute the 
average fasting katabolism per square meter of body surface to 
have been 1044.67 Cals., which agrees fairly well with the average 
computed in Chapter VIII (377), viz., 1089 Cals. per square 
meter. Taking the average of the first and last periods as the basal 
ration, in order to eliminate the effects of the increase in live weight, 
and subtracting it from the results of the intermediate periods, the 
fasting katabolism being estimated in proportion to the surface of 
the animal, the heat increment due to the added nutrients may be 
computed in the manner illustrated for starch in the following table, 
while by correcting the results obtained in the first and last periods for 
the small amount of flesh meal included in the ration, the energy expen- 
diture per gram of dry matter in the barley may likewise be estimated. 

1 Landw. Vers. Stat., 40 (1892), 177. ? Biochem. Ztschr., 55 (1913), iQS- 

3 Landw. Vers. Stat., 84 (1914), 149. 4 Landw. Jahrb., 46 (1914), 499. 



THE PRODUCTION VALUES OF FEEDING STUFFS 655 

Table 197. — Example of Computation of Heat Increment in 

Swine 





Total 
Dry 
Matter 
Con- 
sumed 


Metab- 

OLIZA- 
BLE 

Energy 


Gain by 
Animal 


Com- 
puted 
Heat 
Produc- 
tion 


Esti- 
mated 
Fasting 
Katab- 
olism 


Heat 
Increment 


Starch 


Total 


Per 

Gram 

Dry 

Matter 


Pig 3 

Average of periods i and 6 
Starch by difference . . 


Grams 

1582.2 

1 180.3 

401.9 


Cals. 

5990.32 
4368.40 
1621.92 


Cals. 

2508.19 
1041.03 
1467.16 


Cals. 

3482.13 

3327-37 

IS+-76 


Cals 

2200.71 
2328.68 
-127.97 


Cals. 

1281.42 
998.69 
282.73 


Cals. 

0.810 
0.846 
0.704 



Wellmann, in the course of experiments on the rearing of calves 
and pigs on skim milk and modified skim milk, determined by means 
of comparative slaughter tests the gain of flesh and fat by two pigs 
during twenty-three and thirty-four days respectively, and also col- 
lected the feces and urine quantitatively during the entire period of 
feeding. The energy of the feed and excreta was determined directly. 
Assuming a basal katabolism of noo Cals. per square meter of 
surface (377), the heat increment due to the feed may be computed 
as in previous cases. 

The results of the foregoing investigations are summarized 
in Table 198. One of Wellmann's results, obtained with a 
very restless animal, may be regarded as probably too high and 
has been excluded. In Von der Heide and Klein's experiment 
on palm oil the quantity of fat consumed was relatively large 
as compared with that in Fingerling's experiment on peanut 
oil, although the total ration was not excessive. 

Despite some irregularities, a comparison of these results 
with those for cattle (755) shows clearly that with swine the 
energy expenditure consequent on feed consumption is de- 
cidedly less than with ruminants. Fingerling's results with 
approximately pure nutrients are especially interesting in this 
respect. As regards the more soluble carbohydrates (starch 
and sugar) one can hardly err in ascribing the difference largely 
to the fact that in the comparatively simple digestive organs 
of swine fermentations occur only to a limited extent, while in 
cattle they have been estimated to account for from 9 to 16 per 



6 5 6 



NUTRITION OF FARM ANIMALS 



cent of the total increment in heat production. Straw pulp, on 
the contrary, caused fully as great an increase in the heat pro- 
duction of swine as in that of cattle. Fingerling explains this 
upon the supposition that the straw pulp was fermented rather 
than digested. He failed, however, to find any corresponding 
excretion of methane (745), and Von der Heide, Steuber and 
Zuntz x have observed only a relatively small evolution of com- 
bustible gases from this material in case of the horse. The 
differences as regards oil and protein are not readily explicable 
since, according to Kellner, they are not subject to the methane 
fermentation. 

Table 198. — Increment of Heat Production by Swine 



Grains 



Rice 



Barley . . 
Barley . . 
Dried potatoes 
Flesh meal . 



Mixed rations 

Rice, flesh meal and whey . 
Cockle, barley and maize . 
Rape cake, barley and maize 
Skim milk and flour . . . 



Single nutrients 

Starch 

Cane sugar 

Straw pulp 

Wheat gluten 

Peanut oil 

Palm oil 



Experimenter 



Meissl, et al. 



Meissl, et al. 
Fingerling, et al. 
V. d. Heide and Klein 
Fingerling, et al. 



Meissl, et al. 
Kornauth and Arche 
Kornauth and Arche 
Wellmann 



Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
V. d. Heide and Klein 



Heat In- 
crement 
per 100 

LB. DRY 

Matter 
Eaten 



Therms 




41. 1 

24.4 
27.9 
60.9 



31-93 
47.22 
60.56 
Si-67 
3Q-3S 
105.92 



1 Biochem. Ztschr., 74 (1916), 161. 



THE PRODUCTION VALUES OF FEEDING STUFFS 657 

758. Experiments on the horse. — No experiments on this 
animal have been reported in which the energy expenditure due 
to the consumption of a single feeding stuff has been deter- 
mined. Practically the only data available are those derived 
from the extensive investigations of Zuntz and Hagemann, the 
results of which regarding the fasting katabolism have been 
considered in Chapter VIII (385). On the basis of their ex- 
periments they compute the energy expenditure and the net 
energy value from the composition and digestibility of the 
ration by a method identical in principle with that employed 
in the experiments on cattle already described. The experi- 
ments were conducted so differently, however, as to consti- 
tute practically a distinct method and they may be more 
conveniently considered in connection with the computation of 
net energy values discussed in subsequent paragraphs (775-778) . 

759. Results on carnivora. — Mention was made in Chapter VIII 
(365, 366) of the fact that in carnivora, as well as in herbivora and 
omnivora, the consumption of feed stimulates the heat production, 
the increase having been called by Rubner the specific dynamic 
action. It is evident that experiments like those of Rubner and 
of Lusk were virtually determinations of net energy values for these 
species. While having no direct bearing on the question of the nutri- 
tive values of feeding stuffs for farm animals, these data have been 
extensively quoted in related physiological writings and it seems de- 
sirable to include them here. Rubner's later experiments were made 
at about 33 C, or considerably above the critical temperature for 
the dog, a fact which is of importance in the interpretation of the 
results (395-397). 

A balance experiment with a respiration calorimeter in which 
nearly enough fat was fed to supply the requirement for energy gave 

Table 199. — Increment of Heat Production by Dog on Fat Diet 





Metabolizable 

Energy of 

Feed 


Gaest by Body 


Heat Produc- 
tion 


Fat fed 


Cals. 

53-4 



53-4 
100.00 


Cals. 
-' 7.5 
- 54-0 


Cals. 
60.9 
54-o 


Percentages 


46.5 
87.08 


6.9 
12.92 



2 u 



6 5 8 



NUTRITION OF FARM ANIMALS 



per kilogram live weight the results shown in Table 199, which are 
stated in a form somewhat different from that used by Rubner but 
which in substance are identical with his. 

These figures appear somewhat remarkable in view of the fact 
that the comparison is virtually with body fat. Literally inter- 
preted, it means that the energy of feed fat is only 87 per cent as 
valuable for maintenance as the energy of mobilized body fat plus a 
little protein. If this be true, it implies a larger expenditure of 
energy in the digestion of fat or a greater stimulating effect of the 
resorbed fat upon cell activity than now seems probable, since the 
katabolism of resorbed feed fat can hardly differ greatly from that of 
body fat. Rubner 's figure is the result of a single experiment and 
unfortunately it enters into the computation of all the other results. 
It is a matter of much interest, therefore, that Lusk 1 has found a 
much lower heat increment for fat. In two calorimetric experiments 
in which an emulsion of olive oil was given to a dog he found the 
additional heat elimination to be 0.92 per cent and 1.49 per cent 
of the energy of the oil, so that on the average 98.8 per cent of energy 
of the fat was available for maintenance, a much higher figure than 
Rubner's. 

Both Rubner and Lusk find the most marked effect to be produced 
by protein. In two other experiments by Rubner an amount of lean 
meat nearly sufficient to maintain the dog was fed. The meat con- 
tained a small amount of fat, the average metabolizable energy of 
the feed per kilogram live weight being as follows : — 

In protein 56.70 Cals. 

In fat 4.95 Cals. 

61.65 Cals. 

Using the data afforded by the experiment on fat, the heat incre- 
ment due to the protein may be computed as follows : — 

Table 200. — Increment of Heat Production by Dog on Meat Diet 





Metabolizable 

Energy of 

Feed 


Gain by Body 


Heat Produc- 
tion 


Meat fed 

Fasting 


61.65 Cals. 



— 8.90 Cals. 

— 51.50 Cals. 

42.60 Cals. 
4.31 Cals. 

38.29 Cals. 
67-53 


70.55 Cals. 
51.50 Cals. 


Difference due to fat . . 

Difference due to protein . 
Percentages 


61.65 Cals. 
4.95 Cals. 

56.70 Cals. 
100.00 


19.05 Cals. 
0.64 Cals. 

18.41 Cals. 
3 2 -47 



1 Jour. Biol. Chem., 13 (1912), 38. 



THE PRODUCTION VALUES OF FEEDING STUFFS 659 



Williams, Riche and Lusk report results agreeing substantially 
with those of Rubner when computed in the same way, although 
they regard his method of computation as erroneous. Rubner's 
and Lusk's averages are contained in the following table. It 
should be clearly understood that these figures are not applicable 
to the " digestible nutrients " of the feed of herbivora. 

Table 201. — Percentage of Metabolizable Energy Available 
Average Results for Dogs 





Rubner 


Lusk 




Increment of 
Heat Pro- 
duction 

% 


Available for 
Maintenance 

% 


Increment of 
Heat Pro- 
duction 

% 


Available for 
Maintenance 

% 


Body protein .... 
Meat protein .... 

Gelatin 

Fat . . 

Cane sugar 

Dextrose 


3i-9 

30-9 

28.0 

12.7 

5-8 


68.1 
69.1 
72.0 

87.3 
94.2 


36.O 
1.2 

4-9 


64.O 
98.9 
9S-i 



Net energy values 

In the previous paragraphs there have been considered the 
losses of energy in the excreta and those due to the increased 
heat production which results from the consumption of feed. 
As pointed out in the introductory paragraphs of this section, 
that portion of the gross energy of a feeding stuff which re- 
mains after deducting these two classes of losses constitutes its 
net energy value, or its production value as regards energy. 
Stated in a slightly different way, the net energy value is equal 
to the metabolizable energy minus the increment of heat pro- 
duction. It differs from the relative value, based on the di- 
gestible nutrients or the metabolizable energy, in taking ac- 
count of all the losses of energy to which the feed is subject. 

760. Net energy values for cattle. — It is apparent from the 
foregoing discussions that the data regarding losses of energy 
and net energy values are much more abundant for cattle 
than for any other species of farm animals. Combining the 



66o 



NUTRITION OF FARM ANIMALS 



data of Table 195 (755) regarding the losses due to increased 
heat production with those regarding the losses of chemical 
energy in the excreta recorded in another form in Table 188 
(749) gives the results contained in the following tables, 1 the 

Table 202. — Net Energy Values of Feeding Stuffs for Ruminants 
Per Hundred Pounds of Dry Matter 



Roughage 

Timothy hay 
Red clover hay 
Red clover hay 
Mixed hay . 
Alfalfa hay . 
"Grass hay" 
Meadow hay 
Rowen . . 
Maize stover 
Barley straw 
Oat straw 
Wheat straw 
Straw pulp . 

Concentrates 

Maize meal . . . 
Hominy feed . . 
Wheat bran . . . 
Grain mixture No. 1 
Grain mixture No. 2 
Cottonseed meal 
Linseed meal 
Palmnut meal 
Peanut meal . 
Beet molasses 
Starch . . 
Peanut oil 
Wheat gluten 







Losses 




Incre- 


Experi- 
menters 


Gross 
Energy 


Chem- 
ical 
Energy 
in Ex- 
creta 


Metabo- 

LIZABLE 

Energy 


ment or 
Heat 
Pro- 
duc- 
tion 




Therms 


Therms 


Therms 


Therms 


A&F 


204.94 


120.84 


84.10 


35-47 


A&F 


202.40 


111.63 


90.77 


44-13 


K&K 


— 


— 


79.06 2 


42.27 


A&F 


199.27 


112.45 


86.82 


44-45 


A&F 


198.31 


III. 18 


87-13 


53-03 


K&K 


— 


— 


83-8 3 2 


47.40 


K&K 


201.08 


102.51 


98.57 


56.88 


K&K 


— 


— 


77-34 2 


43-46 


A&F 


196.50 


107.96 


88.54 


48.31 


K&K 


— 


— 


73.672 


39-78 


K&K 


201.22 


129.19 


72.03 


46.00 


K&K 


201.58 


138.89 


62.69 


51.62 


K&K 


188.11 


45-95 


142.16 


52.62 


A&F 


201.49 


50.58 


150.91 


58.33 


A&F 


213.60 


53-84 


I59-76 


61.92 


A&F 


205.57 


91.67 


113.90 


53-39 


A&F 


212.51 


73-53 


138.98 


60.19 


A&F 


209.06 


73-48 


I35-58 


51.76 


K&K 


— 


— 


129.15 2 


44-36 


K&K 


— 


— 


137.72 2 


54-79 


K&K 


— 


— 


124-57 2 


45-68 


K&K 


— 


— 


134-13 2 


52-57 


K&K 


169.80 


42.88 


126.92 


44.82 


K&K 


188.35 


49-95 


138.40 


56.61 


*K&K 


429.00 


188.95 


240.05 


78.34 


K&K 


253-10 


89.58 


163.52 


95.08 



Net 
Energy 
Values 



Therms 

48.63 
46.64 

36.79 
43-37 
34-io 

36.43 
41.69 
33-88 
40.23 

33-89 
26.03 
11.07 
89-54 



92.58 
97.84 
60.51 

78.79 
83.82 
84.79 
82.93 
78.89 
81.56 
82.10 
81.89 
161. 71 
68.45 



1 Penna. Expt. Sta., Bui. 142. 



2 Estimated from digestible organic matter. 



THE PRODUCTION VALUES OF FEEDING STUFFS 66l 

first showing the losses of energy and the net energy values per 
ioo pounds of dry matter and the second the percentage dis- 
tribution of the gross energy of the feeding stuffs between 
the various losses and the net energy values. As already in- 
dicated (745, 749, 756), it appears probable that these values 
may be used also for other classes of ruminants without serious 
error. 

Table 203. — Distribution of Energy of Feed in Ruminants 



Roughage 

Timothy hay .... 

Clover hay 

Mixed hay 

Alfalfa hay 

Meadow hay .... 
Maize stover .... 

Oat straw 

Wheat straw .... 
Extracted straw . . . • 

Concentrates 

Maize meal 

Hominy feed .... 

Wheat bran 

Grain mixture No. 1 . 
Grain mixture No. 2 . 
Beet molasses .... 

Starch 

Peanut oil 

Wheat gluten .... 



Experi- 
menters 


Rejected 

Unused in 

Excreta 


Increment 
of Heat 
Produc- 
tion 




% 


% 


A&F 
A&F 


59 
55 


17 
22 


A&F 


57 


22 


A&F 
K&K 


56 
5i 


27 
28 


A&F 

K&K 

K&K 


55 
64 
69 


25 
23 
26 


K&K 


24 


28 


A&F 
A&F 
A&F 


25 
25 
45 


29 
29 
26 


A&F 


35 


28 


A&F 
K&K 


35 

25 


25 
26 


K&K 
K&K 


27 
44 


30 
18 


K&K 


35 


38 



Net 
Energy 
Value 



% 

24 

23 
21 

17 
21 
20 

!3 

5 
48 



46 
46 
29 

37 
40 

49 
43 
38 

27 



761. Net energy values for swine. — Combining in the same 
form the results of the determinations of the heat increment 
caused by the consumption of feed by swine (757) which are 
recorded in Table 198 and such data regarding the losses of 
energy in feces, urine and methane as are contained in Table 188 
(749) yields the net energy values shown in Table 204 : — 



662 



NUTRITION OF FARM ANIMALS 



Table 204. — Net Energy Values of Feeding Stuffs for Swine 
Per .100 Pounds Dry Matter 



Grains 



Rice 

Barley 

Barley 

Dried potatoes . . 

Flesh meal .... 

Mixed Rations 

Rice, flesh meal and 
whey 

Cockle, barley and 
maize 

Rape, cake, barley 
and maize . . . 

Skim milk and flour 1 

Single Nutrients 

Starch . . . 
Cane sugar . . 
Straw pulp . . 
Wheat gluten . 
Peanut oil . . 
Palm oil . . . 



Experimenters 



Meissl, et al. 
Meissl, et al. 
Fingerling, et al, 
V. d. Heide and 

Klein 
Fingerling, et al, 



Meissl, et al. 
Kornauth and 

Arche 
Kornauth and 

Arche 
Wellmann 



Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
Fingerling, et al. 
V. d. Heide and 
Klein 



Gross 
En- 
ergy 


Losses 

of 
Chem- 
ical 
Energy 
in Ex- 
creta 


Metab- 
oliza- 

BLE 

Energy 


Incre- 
ment 

of 
Heat 
Pro- 
duc- 
tion 


Therms 


Therms 


Therms 


Therms 


206.9 


41. 1 


195-4 
I5I-5 
165.8 


36.7 
29.6 

45-3 


282.6 


44-5 


151-1 
238.1 


49.8 
47-9 


— 


— 


190.7 


41. 1 


— 


— 


162.7 


24.4 


— 


— 


167. 1 
195.9 


27.9 
60.9 


184.3 
I7I-3 
174.3 
249.6 

4I3.0 


i-3 

5-1 
21.7 

45-6 
-4.0 


183.0 
166.2 
152.6 
204.0 
417.0 


3i-9 
47.2 
60.6 

5i-7 
30-3 


— 


— 


420.6 


105.9 



Net 
Energy 
Values 



Therms 

158.7 
121.9 
120.5 

1OI.3 
190.2 



149.6 

138.3 

139.2 
I35-0 



151. 1 

119.0 

92.O 

152.3 
386.7 

3I4.7 



762. Comparison of roughage and concentrates. — The aver- 
age results recorded in the foregoing tables for the total in- 
crease in metabolism resulting from the consumption of a unit 
of dry matter — i.e., for the so-called " work of digestion " 
in the widest sense — are scarcely in accord with common con- 
ceptions. Unconsciously misled by an unfortunate termi- 
nology, we have been accustomed to think of the more coarse 

1 Omitting one very restless animal. 



THE PRODUCTION VALUES OF FEEDING STUFFS 66$ 

and woody feeding stuffs, like hay, straw, stover, etc., as re- 
quiring a greater expenditure of energy in their digestion and 
assimilation than the more concentrated and highly digestible 
grains, for example. It may be somewhat surprising, there- 
fore, to note the relatively small differences in this respect be- 
tween different classes of feeding stuffs, as well as the fact that, 
in case of cattle, the average is distinctly higher for the con- 
centrates than for the roughages, viz., 58.75 Therms per 100 
pounds dry matter as compared with 46.54. While the me- 
chanical work required for the digestion of concentrates is pre- 
sumably less than that necessary in case of roughages on ac- 
count of the greater expenditure for the mastication of the 
latter, this difference appears to be more than compensated for 
by other factors, so that on the whole fully as great an incre- 
ment of the heat production results from the consumption of 
the concentrates. As a class, concentrates are superior to 
roughage, not because their consumption involves a less ex- 
penditure of energy but because they contain more metaboliz- 
able energy, so that more remains available for body use after 
the expenditure has been met. 

763. Differences between feeding stuffs. — But while the 
foregoing results do not show the existence of the great contrast 
between the two chief classes of feeding stuffs in their effects 
on the energy expenditure of the body which seems at times to 
have been assumed, they nevertheless reveal distinct differences 
even between feeding stuffs of the same class. Thus, among the 
hays a distinct increase is found from timothy hay with an 
average heat increment of 35.47 Therms through mixed hay 
and clover hay up to alfalfa, with an average of 53.03 Therms. 
Apparently the legumes cause a distinctly greater increase in 
the metabolism than do the grasses. The chief difference be- 
tween the two seems to lie either in their effect upon the work 
of peristalsis or in the degree to which they stimulate the general 
metabolism. One can hardly doubt that the latter is the 
chief cause and is naturally inclined to associate it with the 
higher percentage of protein in the legumes. That other causes 
may also be operative, however, is indicated by the result on 
maize stover, which is nearly as high as in the case of alfalfa 
and shows a similar distribution among the several factors. 

Among the concentrates there may be noted in particular the 



664 NUTRITION OF FARM ANIMALS 

marked effect of maize in noticeably increasing the metabolism, 
especially during standing. This result is of interest in view 
of Zuntz and Hagemann's observations on the stimulating 
effect of maize upon the metabolism of the horse, which were 
also made on the standing animal, although no increase in the 
minor muscular activity was reported. Grain mixture No. i, 
containing 43 per cent of maize meal, likewise showed a similar 
effect, although with grain mixture No. 2, containing 60 per 
cent of maize, it was much less marked, possibly on account 
of the lower content of protein (12.5 as compared with 17.5 
per cent). 

764. Influence of amount of feed consumed. — In the dis- 
cussions of the foregoing paragraphs it has been tacitly as- 
sumed that both the losses of chemical energy in the excreta 
and the increment of heat production consequent upon feed 
consumption are proportional to the quantity of feed ingested, 
i.e., that the net energy values per unit of feed are substantially 
unaffected by the amount consumed or by the plane of nu- 
trition of the animal. 

This seems not to accord with the general belief that heavy 
rations are relatively less effective than lighter ones and that 
the fat animal utilizes its feed less efficiently than the thin 
one. It became clear, however, in the course of the study, in 
Part III, of the feed requirements for various forms of pro- 
duction, that a variety of factors are influential in determining 
the actual outcome of feeding operations and that diminishing 
returns from heavy or long continued feeding do not neces- 
sarily imply a diminishing efficiency of the feed as a source of 
body material or energy. On the other hand, however, sur- 
prisingly little specific investigation appears to have been de- 
voted to this fundamental question. 

Obviously, differences in the amount consumed might influ- 
ence the net energy value of a feeding stuff either by affecting 
the extent to which chemical energy is lost in the excreta (i.e., 
the metabolizable energy) or by affecting the magnitude of the 
losses due to increased heat production. 

Influence on metabolizable energy. — That in mixed rations the 
digestibility may suffer more or less on heavy feeding has already 
been shown in Chapter XVI (722), notably in Eckles' and Armsby and 



THE PRODUCTION VALUES OF FEEDING STUFFS 665 

Fries' experiments in which decreases of 8 to 10 per cent were observed 
on rations varying in amount by from 42 to 186 per cent, although it 
should be noted that in Armsby and Fries' later experiments only sub- 
maintenance or moderate production rations were used. 

On the other hand, however, it was found in the latter experiments 
that the losses of energy in the methane were distinctly greater on 
the lighter rations so that the differences in the amount of feed con- 
sumed, within the limits of these experiments, failed to show any 
unmistakable effect upon the quantity of energy actually liberated 
in the body from a unit weight of feed. Moreover, it must be borne 
in mind that a considerable amount of the additional energy secured 
by the more extensive fermentation of the lighter ration is liberated 
in the digestive tract as heat of fermentation and does not enter into 
the energy exchange of the body tissues, so that the difference in the 
net nutritive effect is likely to be less than that in the metabolizable 
energy as ordinarily defined. How far such a compensation would 
occur in more liberal feeding is difficult at present to say. 

Influence on heat production. — It is believed by some, however, 
that, aside from differences in digestibility, etc., the metabolizable 
energy actually derived from the feed is less efficiently utilized on 
heavy than on light rations and by fat than by thin animals, i.e., 
that a unit of metabolizable energy supplied yields less product. 
This does not appear exactly probable, a priori. So far as the in- 
creased heat production is due to mechanical work of digestion, it 
would appear that it would be substantially proportional to the 
amount of dry matter consumed, except possibly on extremely heavy 
rations. So far as it is due to a stimulation of the body metabolism 
by the digestive products resorbed (367 e) it would appear more 
likely that, in accordance with the general laws of mass action, it 
would be a diminishing function of the quantity present. Certain 
authors, especially Grafe and Miiller, have, it is true, reported experi- 
ments which are claimed to demonstrate a so-called "luxus consump- 
tion" on heavy rations of carbohydrates, but their results scarcely 
appear to the writer entirely conclusive. 

It has already been shown in Chapter X (450) that any heat 
production arising from a synthesis of body substance, such as that 
of fat from carbohydrates, for example, and which might be supposed 
to result in a decreased efficiency of the feed energy on supermain- 
tenance as compared with submaintenance rations, is apparently not 
sufficient in amount as to materially affect the net energy values of 
feeding stuffs. As regards cattle, the writer has elsewhere 1 discussed 
the results of Kiihn's and Kellner's respiration experiments in their 
bearing on this question, reaching the conclusion that their general 
1 Principles of Animal Nutrition, pp. 466-471. 



666 NUTRITION OF FARM ANIMALS 

tendency seems to be in favor of the hypothesis that the proportion 
of the metabolizable energy utilized is substantially independent of 
the quantity of feed, provided that the changes in the latter are not 
so great as to materially modify the course of the fermentations in 
the digestive tract. Armsby and Fries' results on the same species 1 
tend to confirm these conclusions, since they afforded no distinct evi- 
dence of an increase in the heat production per unit of feed as the 
amount of the latter was increased. 

On the whole the probabilities seem to be that the limit to 
the most efficient use of feed energy, in herbivora at least, is 
set by the capacity of the alimentary canal to digest and as- 
similate feed rather than by the capacity of the organism to 
utilize the material transmitted to it by the organs of resorb- 
tion. If this proves to be the case, the net energy values may be 
regarded as being, if not strictly constant, at least nearly so 
over a wide range of feeding. 

765. Influence of age, breed and individuality. — That dif- 
ferences due to age, breed or " individuality " may exist between 
animals as regards the efficiency with which they utilize the 
energy of their feed and consequently as regards the net energy 
values of the latter does not appear particularly probable a 
priori. Such data on these points as are available have been 
referred to in Chapters XI and XII, the general conclusion being 
reached that the evidence is insufficient to establish the existence 
of any marked differences of this sort except, perhaps, in the 
growth of very young animals. 

766. Influence of kind of production. — It will not have es- 
caped notice that the foregoing data regarding net energy values 
relate entirely to the production of body tissue, whether directly 
in growth or fattening or indirectly in maintenance or in work 
production. While it is perhaps unlikely that the values for 
these various purposes are stricly identical, the discussions in 
Chapters VIII, X, XI, XIV and in the present chapter seem 
to render it probable that the differences are not of sufficient 
magnitude to interfere seriously with the use of these net en- 
ergy values for the computation of rations in practice. 

As regards an important branch of animal husbandry, how- 
ever, viz., milk production, as was shown in Chapter XIII, 
scarcely any accurate data regarding net energy values are yet 

1 Jour. Agr. Research, 3 (1915), 472-476 and Fig. 2. 



THE PRODUCTION VALUES OF FEEDING STUFFS 667 

available, although it appears probable that they are higher 
than the corresponding values for tissue production. A tenta- 
tive method of utilizing the present net energy values in com- 
puting the requirements of dairy cows was there proposed (605), 
but definite experimental data are much to be desired. 

§ 3. The Computation of Net Energy Values 

767. Importance. — It is apparent from the foregoing para- 
graphs that the number of actual experimental determinations 
of net energy values as yet recorded is comparatively small 
and that it can hardly be increased very rapidly, while it is 
obviously impracticable to apply the laborious method of res- 
piration and calorimeter experiments to all the great number 
of feeding stuffs now in use. Determinations of the metabo- 
lizable energy, in which at least the energy of the feeding stuffs 
and of the visible excreta has been determined, are rather more 
numerous, while there are on record the results of a great num- 
ber of digestion experiments in which no determinations of 
energy were made. It is highly important that the mass of 
statistical data thus accumulated, and summarized in tables of 
the composition and digestibility of feeding stuffs, should not 
be incontinently thrown overboard simply because a newer 
point of view has revealed more clearly its deficiencies. On the 
contrary, it should be utilized to the fullest extent possible, in 
connection with the as yet rather meager results of the more 
recent experimental methods, for computing the net energy 
values of such feeding stuffs as have not yet been subjected 
to direct investigation. 

Computation from digestible nutrients 

768. Kellner's investigations. — To Kellner is due the first 
attempt to make practical application of the conception of the 
feed as the source of energy to the body. In 1880, in his in- 
vestigations upon the relations between muscular activity and 
metabolism in the horse (637) he determined the additional 
amount of work, which the animal was able to perform as a 
result of the addition to his rations of starch and of fat. He 
expressed his results in terms of the percentage of the energy 



668 



NUTRITION OF FARM ANIMALS 



of the starch or fat which was recovered as useful work and 
called attention to the desirability of determinations of the 
heats of combustion of nutrients and feeding stuffs. Sixteen 
years later, after Rubner had published his fundamental work 
on the replacement values of nutrients, and Zuntz and his as- 
sociates (385, 651-656) had begun their investigations upon the 
metabolism of the horse from the standpoint of energy, Kellner 
was able to return to the subject and undertake the extensive 
investigations with cattle frequently cited on previous pages. 

769. Energy values of digestible nutrients. — Taking as his 
point of departure the digestible nutrients of feeding stuffs, 
Kellner sought first to determine the net energy values of the 
digestible protein, carbohydrates and fats for cattle by adding 
these substances in as pure form as possible to a basal ration in 
the manner already described (449). The results with cattle 
obtained in this way on starch, straw pulp, sugar, wheat gluten 
and oil are included in Table 202 (760) . In that table, however, 
these materials are regarded in the light of feeding stuffs and 
the energy losses and net energy values relate to the substance 
as a whole and include all its effects. For his purpose, how- 
ever, Kellner computed the net energy values, not of these sub- 
stances as a whole but of the protein, carbohydrates and fat 
which determinations of digestibility showed to have been 
resorbed from them, with the following results. 1 

Table 205. — Net Energy Values of Digestible Nutrients for 

Cattle 



Protein 

Starch and crude fiber 

Cane sugar 

Ether extract 

of roughage 

of grains and their by-products .... 

of feeding stuffs containing over 5 per cent 
fat 



Per 100 Pounds 
of Dry Matter 



Therms 

IOI.6 

107. 1 

8l.2 

204.I 
227.3 

258.6 



Per Cent 

of Metab- 

olizable 

Energy 



45-8 
64.1 
51.6 

S4-i 
56.8 

64.6 



x Landw. Vers. Stat., 53 (1900), 1-474; Ernahrung landw. Nutztiere, 6th Ed., 
95-159- 



THE PRODUCTION VALUES OF FEEDING STUFFS 669 

Obviously the percentages in the last column are analogous 
to those obtained by Rubner and by Lusk (759) in experi- 
ments on dogs, and the differences between the two sets em- 
phasize the differences in the nutritive processes of the two 
species. 

770. Correction for crude fiber. — Kellner then proceeded to 
test the applicability of these factors to the ordinary feeding 
stuffs of cattle. With a certain number, notably the oil meals, 1 
the net energy values as computed by the use of his factors 
from the amounts of protein, carbohydrates and fat actually 
digested showed a close agreement with those found in direct 
experiments with the respiration apparatus. The digestible 
nutrients of these materials were of full value as compared with 
pure starch, gluten or oil. 

Table 206. — Net Energy Values of Oil Meals for Cattle 
Per 100 Pounds Dry Matter 



Cottonseed meal 
Peanut meal 
Palmnut meal . 
Linseed meal . 



Computed 


Observed 


Therms 


Therms 


86.4 


84.8 


81.4 


81.6 


77-3 


78.9 


84.7 


82.9 



Difference 



% 

- 1.8 
+ 0.2 
+ 2.0 

— 2.1 



On the other hand, a striking contrast with the oil meals is 
afforded by the roughages, whose net energy values as directly 
determined were much lower than those computed, the deficit 
ranging from 30 per cent to 80 per cent and being greatest 
with the coarsest and least digestible materials. 2 Kellner found 
this deficit to be more nearly proportional to the crude fiber 
than to any other ingredient of the feeding stuffs, ranging 
from 46.3 Therms to 76.7 Therms per 100 pounds of total fiber. 
By subtracting the average of 61.7 Therms from the computed 
net energy values, results were obtained which agreed well 
with those secured in direct experiments in the case of the 
hays but still showed considerable discrepancies for the straws, 
as follows : — 



1 Loc. cit., p. 160. 



2 Ibid., p. 162. 



670 



NUTRITION OF FARM ANIMALS 



Table 207. — Net Energy Values of Roughages for Cattle 
Per 100 Pounds Dry Matter 



Wheat straw 

Sample a . 

Sample b . 
Oat straw 
Barley straw 
Meadow hay 

Sample a . 

Sample b . 
Clover hay . 
"Grass hay" 
Rowen . . 



Computed 
with Cor- 
rection 
for Crude 
Fiber 


Observed 


Therms 


Therms 


16.1 


9.1 


7-5 


10.4 


23.0 


28.5 


28.4 


33-9 


35-4 


3S-o 


48.3 


47.1 


35-3 


36.8 


39-4 


36-7 


36.1 


33-9 



Differ- 
ence 



Per Cent 

- 43-4 
+ 38.0 
+ 24.1 
+ 19.5 

- i-3 

- 2.5 
+ 4.1 

- 7-o 

- 6.0 



For finer materials like chaff, presumably requiring a less 
expenditure for mastication, 31.8 Therms per 100 pounds of total 
crude fiber was deducted. For green forage containing 16 per 
cent or more of crude fiber the same deduction was made as for 
dry forage and for that containing 4 per cent or less of crude 
fiber, the same as for chaff, while between these limits a sliding 
scale was used. This correction for crude fiber was applied 
only to roughage. 

Kellner ascribed this apparent effect of crude fiber largely 
to the mechanical work required for its mastication and trans- 
portation through the alimentary canal, but in part also to the 
fermentations to which it is subject ; in other words, he ascribed 
it to the so-called " work of digestion." In reality, however, 
the crude fiber can be regarded only as a convenient empirical 
measure of the differences between concentrates such as the 
oil meals and roughage. It has already been shown from Kell- 
ner's own experiments and from others (762) that the loss of 
energy in this way, far from being greater, is on the whole rather 
less with roughages than with concentrates and that the me- 
chanical work of the digestive organs is probably a rather small 
factor in it. Roughages have relatively less net energy value, not 



THE PRODUCTION VALUES OF FEEDING STUFFS 671 

because they contain much crude fiber which causes much me- 
chanical work but because the feeding stuff as a whole stimulates 
the metabolism and causes a loss of energy which, though not 
greater, or, it may be, even less, than in the case of concentrates, 
is deducted from a much smaller amount of metabolizable energy 
supplied by the less amount of substances digested. 

771. Relative values for concentrates. — That the crude fiber 
is far from being the only determining factor of the amount of 
energy. expended in consequence of feed consumption is clearly 
shown by the majority of Kellner's experiments on concentrates 
and roots. Although with the oil meals a close agreement of 
the observed and computed results was obtained, in most in- 
stances the observed net energy value fell considerably short of 
that computed by the use of the factors of Table 205. The fol- 
lowing table contains the results of the comparisons thus far 
reported. 1 They show clearly that the digestible organic 
matter has a very unequal value in different classes of feeding 
stuffs, but a comparison with the percentages of crude or of 
digestible nutrients also shows that the crude fiber fails in 
these cases as a measure of the differences. 

Table 208. — Observed Net Energy Values for Cattle as Per Cent 

of Computed 

Rye meal 93.5 per cent 

Bean meal 94.4 per cent 

Rye bran 79.0 per cent 

Wheat bran 77.3 per cent 

Dried brewers' grains 84.3 per cent 

Dried distillers' grains 88.2 per cent 

Rice meal 108.4 per cent 

Malt sprouts 85.8 per cent 

Potatoes 98.0 per cent 

Mangolds 86.9 per cent 

Fresh beet pulp 94.1 per cent 

Dried beet pulp 78.4 per cent 

In computing the net energy values of concentrates, there- 
fore, Kellner made no correction for the crude fiber, but instead 
corrected in each case the value computed from the digestible 
nutrients by multiplying it by a percentage (Wertigkeit) taken 
directly from the foregoing table when possible or estimated 



Ernahrung landw. Nutztiere, pp. 165-167. 



672 NUTRITION OF FARM ANIMALS 

from it. For example, the net energy values of alfalfa hay and 
of wheat bran having the composition and digestibility given 
by Allen * would be computed as follows : — 

Table 209. — Computation of Net Energy Values per 100 Pounds 

According to Kellner 

Alfalfa Hay 

Digestible protein 10.58 X 1.016 = 10.75 Therms 

Digestible carbohydrates 37.33 X 1.071 = 39.98. Therms 

Digestible ether extract 1.38 X 2.041 = 2.82 Therms 

53.55 Therms 

Total crude fiber 25.00 X 0.617 = 15.43 Therms 

Net energy value 38.12 Therms 

Wheat Bran (Relative Value 77 %) 

Digestible protein 12.01 X 1.016 =12. 20 Therms 

Digestible carbohydrates 41.23 X 1.07 1 = 44.16 Therms 

Digestible ether extract 2.87 X 2.273 = °-5 2 Therms 

62.88 Therms 
Net energy value 62.88 X 0.77 = 48.42 Therms 

772. Starch values. — Kellner's results were in reality net 
energy values, as is evident from the method by which they 
were obtained. In order, however, to avoid the use of the 
large numbers required to express the net energy values of 
rations in Calories,. and also to avoid the introduction of un- 
familiar terms, he converted them for practical use into what he 
called " starch values." The starch value of a feeding stuff 
may be briefly defined as the amount of pure starch (assumed to 
be perfectly digested) which has the same net energy value. 
Thus, Kellner's table gives the starch value of maize meal as 
81.5 kilograms per 100 kilograms, or 81.5 pounds per 100 pounds. 
One pound of starch, according to Kellner's results (769), has a 
net energy value of 107 1 Cals. The starch value of 81.5 given 
for maize meal, therefore, is equivalent to a net energy value 
of 1071 X 81.5 = 87,286 Cals., or 87.29 Therms, per 100 pounds 
and conversely the starch values of the alfalfa hay and wheat 
bran of the previous paragraph would be 35.59 and 45.21, re- 
spectively. 2 

1 U. S. Dept. Agr., Farmers' Bulletin 22 (Rev.), iooi, pp. 8-9. 

2 In other words, Kellner's starch values multiplied by 1.071 = net energy 
values per 100 lb. 



THE PRODUCTION VALUES OF FEEDING STUFFS 673 

Kellner's starch values yield numbers of the same order of 
magnitude as those already familiar in tables of digestible nu- 
trients and avoid unfamiliar units. They accomplish these 
ends, however, by ignoring the whole conception on which the 
system is built up, while some striking instances in recent lit- 
erature have shown that it is not always easy, even for ex- 
perts, to avoid confusion of thought in connection with their 
use. It appears to the writer to have been an unfortunate con- 
cession to attempt to express quantities of energy in terms of 
matter. He believes the intelligent feeder can readily learn 
to use units of energy in his computation of rations, as not a 
few have already done, and that there are manifest advantages 
in going over frankly and boldly to a system based on energy, 
while the objection to the use of large numbers is readily avoided 
by the employment of a larger unit of energy, the Therm (308). 
Net energy values expressed in Therms per 100 pounds are of 
the same order of magnitude as the familiar figures for di- 
gestible nutrients, and even if 100 kilograms be made the 
basis of calculation they are not inconveniently large. For 
these reasons, energy values of feeding stuffs in the present 
volume are expressed in Therms per 100 pounds. 



Computation from digestible organic matter 

773. Independent of chemical composition. — It is apparent 
from the foregoing description of Kellner's somewhat compli- 
cated method that it is essentially based on the digestible 
protein, carbohydrates and fats of the older relative values 
(705-710), while it involves in its execution certain more or 
less empirical corrections which are at bottom simply methods 
of applying the average net results on typical feeding stuffs 
to other materials. Armsby and Fries * have proposed a 
method which seeks to attain the same end more directly and 
simply, relating the energy content and the necessary deduc- 
tions to the total dry matter or total digestible matter of the 
feeding stuff independently of its chemical composition. 

The energy content of a feeding stuff is just as definite a 
quantity as its content of protein, carbohydrates, or fats, and 

1 Jour. Agr. Research, 3 (1915), 486. 
2 X 



674 NUTRITION OF FARM ANIMALS 

it is entirely possible to trace the distribution of that energy 
in the body quite independently of any knowledge of the chemical 
composition of the material. Not only so, but it is believed 
that in discussing energy values there are distinct advantages 
as regards simplicity, and perhaps also as regards accuracy, in 
cutting loose as far as possible from the conventional data re- 
garding chemical composition and digestion coefficients and in 
dealing directly with quantities of energy. 

This statement is by no means to be understood to stigmatize 
comparisons based on chemical methods as either valueless or super- 
fluous. The problems of nutrition are too complex and too difficult 
for us to refuse any light that can be thrown on them by any method, 
and the energy relations touch only one phase of them. The point 
is that in whatever degree their energetic aspects can be separated 
from their chemical aspects, to that extent we possess two inde- 
pendent methods of approach to them. 

774. Method of computation. — As already pointed out, 
the net energy value of a feeding stuff is equal to its me- 
tabolizable energy minus the heat production caused by its 
consumption. It has been shown (753) that the metabolizable 
energy of a feeding stuff, when not determined directly, may 
be computed approximately from the total digestible organic 
matter by multiplying by a proper factor. If from this 
result there be subtracted the energy expenditure due to 
feed consumption, either as directly determined or as esti- 
mated from that of similar feeds, the remainder is approx- 
imately the net energy value. Thus in the same two feeding 
stuffs just used to illustrate Kellner's method each pound of di- 
gestible organic matter, according to the averages on previous 
pages (753-755), would contain i.6o Therms of metabolizable 
energy in the hay and 1.77 Therms in the bran; the average 
losses of energy in heat production per pound of dry matter 
would be for the hay 0.5303 Therm and for the bran 0.5339 
Therm, and the computation of the net energy values would be 
as follows : * — 

1 The digestible protein, carbohydrates and fats enter into the calculation simply 
as a means of obtaining the total digestible organic matter when, as is usually the 
case, this is not reported separately. If the latter is the case, then the computa- 
tion is, as stated above, independent of the chemical composition. 



THE PRODUCTION VALUES OF FEEDING STUFFS 675 



Table 210. — Computation of Net Energy Values per 100 Pounds 
According to Armsby and Fries 



Total dry matter 

Digestible 

Protein . . . 
Carbohydrates 
Fats . . . . 



Total digestible organic 
matter .... 

Metabolizable energy . 
Loss in heat production 

Net energy value . . 



Alfalfa Hay 



91.6 lb. 

10.58 lb. 

37-33 lb. 

1.38 lb. 

49.29 lb. 

49.49 X 1.60 = 78.86 Therms 

91.60 X 0.5303 = 48.58 Therms 

30.28 Therms 



Wheat Bran 



88.5 lb. 

12.01 lb. 

41.23 lb. 

2.87 lb. 

56.11 lb. 

56.11 X 1.77 = 99.31 Therms 

88.50 X 0.5339 = 47.25 Therms 

52.06 Therms 



The same method of computation is of course applicable to 
other species than cattle, so far as the meager data at hand 
permit. The results of such computations, based upon the 
average composition and digestibility of American feeding 
stuffs, are contained in the tables of the Appendix. 



Computation of net energy values for the horse 

775. Zuntz and Hagemann's method. — The method em- 
ployed by Zuntz and Hagemann x for computing net energy 
values for the horse (758) is substantially similar to that just 
illustrated for cattle. The metabolizable energy is estimated 
from the digestible nutrients and from it is subtracted the com- 
puted energy expenditure due to the consumption of the feed. 

776. Metabolizable energy. — From the results of five digestion 
and metabolism experiments on rations of oats, hay and straw in 
different proportions made at intervals between 1888 and 1891, they 
compute the metabolizable energy of the total digestible nutrients 
(including the digested fat multiplied by 2.4) to average 3.96 Cals. 
per gram, corresponding to 3.99 Cals. per gram digestible organic 
matter as computed by the writer in Table 188 (749). In the 
respiration experiments, the digestible nutrients were not determined 
directly but were estimated by combining the results of the same 
five digestion and metabolism experiments in various ratios according 
to the proportion of oats, hay and straw consumed. 

777. Increment of heat production. — Experiments upon man, 
made by Magnus-Levy in Zuntz's laboratory, had previously shown 

1 Landw. Jahrb., 27 (1898); Ergzbd. Ill, 211-236, 276-279, 418. 



676 NUTRITION OF FARM ANIMALS 

that food consumption increased the total metabolism by about 9 per 
cent of the metabolizable energy of the food eaten. Zuntz and Hage- 
mann assume that this result is applicable to the digestible nutrients 
of the feed of the horse. 

In addition, it was found that hay produced a much more marked 
effect than did grain in augmenting the heat production of the horse 
as estimated from the respiratory exchange, which was determined 
by means of the Zuntz apparatus in short periods at various intervals 
after the consumption of more or less diverse rations, a small correc- 
tion being added for cutaneous and intestinal respiration. This dif- 
ference is ascribed to the crude fiber of the hay and its amount is 
computed to be 2.086 Cals. per gram. The energy expended in the 
mastication of the feed is likewise related to its crude fiber content, 
being estimated at 0.565 Cals. per gram. The total heat increment 
per gram of crude fiber, therefore, is estimated at 2.65 Cals. per gram. 

778. Computation of net energy value. — In brief, Zuntz 
and Hagemann compute the heat production due to the con- 
sumption of feed by the horse to be equal to 9 per cent of 
the metabolizable energy, estimated at the rate of 3.96 Cals. 
per gram of digestible nutrients, plus 2.65 Cals. for each gram 
of total crude fiber present, and by subtraction of these amounts 
from the metabolizable energy obtain the net energy value. 

The method of computation may be conveniently illustrated 
from the data given by Langworthy * for timothy hay. Zuntz 
and Hagemann's factors, recalculated per 100 pounds for 
convenience, become for metabolizable energy 1.796 Therms 
and for crude fiber 1.202 Therms. On this basis the calculation 
of the heat production due to the hay would be as follows : — 

Table 211. — Computation or Net Energy Value per 100 Pounds 

for the Horse 

Digestible nutrients 

Protein 1.25 lb. 

Crude fiber 12.39 lb. 

Nitrogen-free extract 21.29 lb. 

Fat (1.18 X 2.4) 2.83 lb. 

37-72 lb. 
Total crude fiber 29.00 lb. 

Metabolizable energy 1796 Therms X 37.72 = 67.75 Therms 

Increase of metabolism 
9 per cent of metabolizable energy 67.75 Therms X 0.09 = 6.10 Therms 
Additional for crude fiber . . . 1.202 Therms X 29.00 = 34.86 Therms 
Total 40.96 Therms 

Net energy value 26.79 Therms 

1 U. S. Dept. Agr., Office of Expt. Stas., Bui. 125, p. 14. 



THE PRODUCTION VALUES OF FEEDING STUFFS 677 

As is evident from the methods by which the factors were 
reached, this method of calculation is not strictly exact, but the 
authors believe it to be a sufficiently close approximation on 
which to base computations of rations in practice. 

Zuntz and Hagemann's method of computation has been the subject 
of considerable criticism, the two principal points being, first their 
estimate, based upon the results of experiments on man, of 9 per cent 
for the effect of the digestible nutrients, and second, and more es- 
pecially, the assumption that the metabolism for 24 hours may be com- 
puted from the results of comparatively short respiration experiments. 
Qualitatively, Zuntz and Hagemann have clearly demonstrated 
the very considerable increase of energy metabolism in the horse 
during the digestion of his feed, as well as the fact that this increase 
is relatively greater with roughage than with grain, and they were 
the first to point out that this effect must be taken into account in 
estimating the values of feeding stuffs. There may be a difference 
of opinion as to the quantitative accuracy of their figures and cer- 
tainly investigations by more direct methods, involving fewer assump- 
tions and complex calculations, are greatly to be desired, but until 
such results are obtained, we may continue to use provisionally those 
reached in the manner just described. 

1 779. Wolff's method of computation. — His extensive investiga- 
tions upon the working horse made at Hohenheim in 1877 to 1894 
and antedating the investigations thus far mentioned, led Wolff to 
a still simpler approximate method of estimating the relative net 
energy values of feeds for the horse. 

It was shown, on the average of a considerable number of compari- 
sons, that the digestible nutrients from roughage were less efficient 
both for work production and for maintenance than were those derived 
from grain. Wolff found, however, that if the digestible crude fiber 
were omitted from the comparisons, the ratio between the fiber-free 
nutrients and the work performed was comparatively uniform and 
also that this assumption yielded uniform results for the amount of 
fiber-free nutrients necessary for maintenance. He therefore con- 
cluded that the crude fiber in the rations of the horse was apparently 
valueless and that the remaining digestible nutrients might be re- 
garded as of equal value whether derived from grain or from roughage. 
Expressed in the light of our present conceptions, this is practically 
equivalent to saying that the net energy value is proportional to the 
amount of fiber-free nutrients. 

Wolff is careful to say that the digestible crude fiber is apparently 
valueless, and virtually regards the amount of crude fiber as furnish- 
ing a convenient empirical measure of the difference in the value of 



678 NUTRITION OF FARM ANIMALS 

the digestible nutrients of roughage as compared with those of grain. 
That such is the case is doubtless explained in part by the rather 
limited variety of feeding stuffs employed in the experiments. The 
roughage was meadow hay with, in some cases, a small addition of 
straw, while the grain was usually oats, partially replaced in some 
instances by other feeds. Whether the same relation between fiber- 
free nutrients and work done would hold in widely different rations 
is not apparent. 

Wolff's results are relative only. They do not show the actual 
amount of net energy in the rations but only that it was proportional 
to the fiber-free nutrients. The energy content of the latter would 
differ considerably from the net energy as computed by Zuntz and 
Hagemann's method, first because it does not include the deduction 
of 9 per cent of the metabolizable energy, and second, because it 
assumes a uniform value of zero for crude fiber, while Zuntz and Hage- 
mann's method gives the crude fiber a negative value if it has a di- 
gestibility of less than 55 per cent. Values computed according 
to Wolff's method from the fiber-free nutrients would therefore con- 
siderably exceed Zuntz and Hagemann's figures. 



§ 4. Production Values as Regards Protein 

Relative values of proteins 

780. Differences in proteins. — As appears from the discus- 
sions of the preceding section, the production values of feeding 
stuffs as regards energy may already be formulated with some de- 
gree of accuracy, although further investigation is much needed. 

Concerning the production values as regards protein, the 
situation is far less satisfactory. For years the protein of 
feeding stuffs has been treated as if it were a single chemical 
substance ; i.e., the different proteins known to exist in feeding 
stuffs have been assumed to have substantially equal nutritive 
values. The more recent investigations into the chemistry 
and physiology of the proteins, however, have resulted in an 
entire change in the point of view. As has been fully shown 
in previous chapters (340, 398, 465, 552), it is the constituent 
amino acids into which the proteins are split in digestion which 
are the materials out of which body protein is constructed, and 
the processes of maintenance, growth or milk production re- 
quire for their support, not proteins as such, but certain 
amounts and proportions of such of the amino acids as cannot 



THE PRODUCTION VALUES OF FEEDING STUFFS 679 

be synthesized in the body. In place of a single requirement for 
protein, it would appear that there must be substituted a num- 
ber of separate amino acid requirements, a deficiency as regards 
any one of which may constitute a limiting factor. 

781. Incomplete and unbalanced proteins. — As appeared 
in Chapter I (50) certain vegetable proteins may be classed 
as incomplete proteins in the sense that they lack entirely 
one or more of the amino acids characteristic of proteins in 
general. The classic example of an incomplete protein is 
gelatin, which lacks tyrosin and tryptophan and which has 
long been known to be incapable by itself of maintaining the 
stock of body protein in an animal. A similar case among the 
vegetable proteins which has been much discussed is the zein 
of maize, which yields neither lysin, glycin nor tryptophan on 
hydrolysis and which is incapable of supporting either main- 
tenance (399) or growth (465). Still another instance is afforded 
by the gliadin of wheat (465), which lacks lysin and which, 
while adequate for maintenance, is unable to support growth. 
Furthermore, the proteins of the cereal grains in general, while 
not incomplete in the sense of absolutely lacking certain amino 
acids, may, from the standpoint of animal nutrition, be called 
unbalanced in that, as compared with the body proteins, they 
are relatively rich in glutamic acid and therefore correspondingly 
deficient in other constitutents, including those ingredients 
which, like lysin in particular, appear to be essential to growth. 
It appears evident that in the conversion of a unit weight of 
such a protein into body protein, a considerable portion of the 
amino acid present in excess must undergo deaminization (233) 
and be substantially a waste product so far as the protein re- 
quirement of the body is concerned, although it may of course 
serve as a source of energy. Quantitative results as to the 
maximum percentage utilization of individual proteins, how- 
ever, are not yet available. 

782. Application of results. — But while the general validity of 
the newer point of view seems well established, it does not appear 
possible as yet to utilize it in establishing net protein values for 
feeding stuffs comparable to the net energy values discussed in 
§ 2 of this chapter. For this there are three principal reasons. 

First, sufficient knowledge of the proteins of feeding stuffs 
is lacking. Although the constituents of a considerable number 



680 NUTRITION OF FARM ANIMALS 

of vegetable proteins derived from seeds is known, those con- 
tained in roughages and in roots have not yet been investigated, 
although a beginning has been made l in determining the pro- 
portions of the different groups of amino acids which are yielded 
by the total nitrogenous matter (crude protein) of various feed- 
ing stuffs. 

Second, as has appeared in previous chapters, such informa- 
tion as is available respecting the protein requirements of farm 
animals has been derived from experiments in which only the 
total protein supplied was considered without reference to its 
kind. Practically no knowledge is available as to the amino acid 
requirements of the various farm animals for different purposes. 

Third, even were the production values of the various single 
proteins known, it would not be possible to estimate from them 
the production values of the mixed proteins of feeding stuffs, 
since a deficiency in one protein might be compensated by a 
surplus in another and the mixture show a much higher pro- 
duction value than either of its ingredients separately. Thus, 
as already noted, the value of wheat gliadin, which lacks lysin, 
is practically zero for growth, while as part of a mixture with 
other proteins supplying lysin it may have a high value, the 
replacement of 25 per cent of it by lactalbumin, for example, 
rendering the mixture fully adequate to support normal growth. 
Each particular mixture of proteins would have its own pro- 
duction value, which might differ widely from the mean of the 
values for the individual constituents. 

The qualitative differences in proteins are doubtless of much 
significance, and the researches in progress can hardly fail 
ultimately to lead to a more rational method of valuation than 
that now in use, but as yet they do not afford an adequate 
basis for expressing the values of feeding stuffs in general as 
sources of protein. For the purposes of the stock feeder, there- 
fore, it still seems necessary to adhere to the older method which 
regards the digestible protein of a feeding stuff as expressing 
approximately its production value in this respect, thus vir- 
tually assuming that in ordinary mixed rations the protein 
deficiencies of the different ingredients will largely balance each 
other, and this method has been followed in the tables of the 

1 Grindley, Joseph and Slater; Jour. Amer. Chem. Soc, 37 (1915), 1778 and 
2762: Nollau; Jour. Biol. Chem., 21 (1915), 611. 



THE PRODUCTION VALUES OF FEEDING STUFFS 68 1 

Appendix. This should be done, however, with a distinct 
consciousness of the inadequacy of the method and with the 
hope that it may ultimately be replaced by one having a more 
scientific basis. 

Meanwhile, notice should be taken of the results of several 
recent investigations upon the mixed proteins of a few feeding 
stuffs, particularly those of the cereal grains. 

783. Low value of maize proteins. — The demonstration of 
the insufficiency of the zein of maize for either maintenance 
or growth (781) has tended not unnaturally to produce the 
impression that this important feeding stuff is relatively 
valueless as a source of protein. Zein, however, is not the only 
protein of maize. According to Osborne and Mendel 1 the mixed 
proteins of maize are made up approximately as follows : — 

Zein . 41 % 

Maize glutelin 31% 

Globulins, albumins and proteoses 22% 

Insoluble in alkali 6 % 

100% 

Glutelin yields all the amino acids which zein lacks and 
the same is probably true of the other proteins of maize. Evi- 
dently the results of experiments on zein do not show maize 
to be valueless as a source of protein, although they do indicate 
a relatively low value and this conclusion has been confirmed by 
the experiments of Osborne and Mendel on rats and of Waters 
on pigs. On the other hand, however, Hart and McCollum 2 
were able to obtain a normal growth of pigs on rations supply- 
ing only maize protein but supplemented by salts. 

Osborne and Mendel ! have investigated the nutritive value of the 
mixture of proteins contained in the "corn gluten" produced in the 
manufacture of starch from maize and consisting chiefly of zein and 
glutelin in the proportion of approximately 100 to 44. In such a 
mixture, the deficiencies of the zein are to a greater or less extent 
compensated for by the glutelin, and the mixed proteins not only 
proved adequate for maintenance but were able to support rather 
slow growth. The addition to them of lactalbumin or of casein, 
however, rendered them much more efficient and induced normal 
growth. 

'Jour. Biol. Chem., 18 (1914), 1. 2 Ibid., 19 (1914), 373- 



682 



NUTRITION OF FARM ANIMALS 



Waters * in experiments on growing pigs has shown in a striking 
manner the practical significance of Osborne and Mendel's results. 
In each of the four trials reported, one lot of animals received only 
maize. The others were given maize with the addition of ash in- 
gredients, either by direct additions of salts or in the form of the so- 
called protein-free milk, while still others received an addition of 
complete proteins, as nearly ash-free as possible, derived in some 
cases from blood and in others from milk. The growth of the lots 
receiving only maize was either very slow or practically zero and the 
same was true when ash was added, showing that the failure to grow 
was not due to a lack of mineral matter. When, however, com- 
plete proteins were added to the maize, steady and normal growth 
took place and comparative analyses of the carcasses showed a cor- 
responding storage of body protein by the animals. The total re- 
sults as to live weights were as follows : — 

Table 212. — Influence of Nature of Protein Supply on Growth 

of Pigs 



Second trial 

Maize alone 

Maize and ash 

Maize and blood albumin . . 
Maize, blood albumin and ash 

Third trial 

Maize alone 

Maize and ash 

Maize and protein-free milk 
Maize and milk protein . . . 
Fourth trial 

Maize alone 

Maize and ash 

Maize and protein-free milk 
Maize and milk albumin . . 
Maize and casein 

Fifth trial 

Maize alone 

Maize and milk ash . . . . 
Maize and tryptophan . . . 
Maize and milk albumin . . 
Maize and casein 



Length of 


Initial 2 


Final 


Trial 


Weight 


Weight 


Days 


Lb. 


Lb. 


280 


50 


108 


280 


5o 


102 


280 


50 


330 


280 


50 


362 


187 


50 


51 


187 


5o 


SO 


187 


5o 


38 


187 


5o 


334 


180 


5o 


117 


180 


5o 


108 


180 


50 


141 


180 


So 


239 


180 


5o 


291 


200 


30 


79 


200 


30 


55 


200 


30 


74 


200 


30 


268 


200 


30 


232 



Daily 
Gain 



Lb. 

O.21 
0.19 
1.00 
1. n 

o. 

o. 

- 0.06 

1.50 

o-37 
0.32 
0.51 

1.05 
1-34 

0.25 
0.13 
0.22 
1. 19 
1. 01 



1 Proc. Soc. Prom. Agr. Sci. (1014), p. 7. 

2 Approximate. The exact initial weights are not given in the report cited. 



THE PRODUCTION VALUES OF FEEDING STUFFS 683 

784. Values of other cereal proteins. — Investigations at the 
Wisconsin Experiment Station led to the conclusion that not 
only the proteins of maize but the unbalanced proteins of other 
cereal grains are distinctly inferior to milk proteins as sources 
of protein for growth and milk production. 

Hart, Humphrey and Morrison * in two comparisons of maize and 
alfalfa proteins for growing heifers observed a retention of approxi- 
mately 20 to 24 per cent of the maize nitrogen as compared with 
much higher figures obtained for milk proteins in later experiments 
at the same institution. 

McCollum 2 reports a series of trials on young pigs in which the 
effects of the proteins of maize, wheat and oats, of casein and of skim 
milk on the nitrogen balance were compared. The protein supply 
varied in the different trials but the author presents reasons for believ- 
ing that in no case did it exceed the amount the animal was capable 
of utilizing in growth, so that the results are not affected in the 
manner discussed in Chapter XI (468) by surplus protein being 
katabolized. On the higher protein rations, from 20 to 34 per cent 
of the resorbed nitrogen was retained in the body of the animal, 
while, contrary to what would naturally be expected, the percentage 
retention was decidedly lower on rations supplying less protein. 
The milk proteins, on the other hand, showed a decidedly higher per- 
centage retention, viz., for casein 51 per cent and for skim milk pro- 
teins 66 per cent. 

Hart and Humphrey 3 have compared the proteins of maize, wheat, 
gluten feed, oil meal, distillers' grains and milk as sources of protein 
for milking cows (587). Unfortunately, the effects were chiefly on 
the body protein, so that the only comparison possible is between 
the algebraic sums of body protein and milk protein. Computed in 
this way, the average percentage efficiency for three animals was, 
for milk proteins, 59, for maize 40, for wheat 36, for gluten feed 45, 
for oil meal 61 and for distillers' grains 60. 

785. Alfalfa proteins. — Hart, Humphrey and Morrison in 
their comparisons of maize and alfalfa proteins just men- 
tioned (784), found the total nitrogen of alfalfa to show about 
the same percentage retention in both growth and milk pro- 
duction as did the total nitrogen of maize. 

In none of these Wisconsin experiments is the maintenance 
requirement of the animals taken into account in computing 

1 Jour. Biol. Chem., 13 (1912), 133. 2 Ibid., 19 (1914), 323. 

3 Ibid., 21 (1915), 239; 26 (1916), 457- 



684 NUTRITION OF FARM ANIMALS 

the percentage efficiency of the protein. If this be done, using 
the approximate data contained in Chapter IX (415-417), the 
percentages of the proteins supplied in excess of maintenance 
which were retained would be distinctly increased in every case. 
It cannot be concluded, therefore, that the low percentages 
computed by the Wisconsin investigators show that only these 
rather small proportions of the cereal proteins are capable of 
transformation into body proteins. On the other hand, how- 
ever, such a conjectural correction would result in making the 
relative differences between the different proteins appear 
greater than those shown by the method of calculation used. 

No other studies upon the relative values of the mixed pro- 
teins of feeding stuffs have come to the writer's notice. 

Value of non-protein 

In a previous paragraph (782) the conclusion was reached 
that for the present the only available measure of the protein 
values of feeding stuffs is the total amount of digestible pro- 
tein which they contain. In the application of this method 
itj becomes necessary to decide whether the basis of compari- 
son shall be the " crude " protein or the " true " protein as de- 
termined by existing conventional methods (104-107) ; in other 
words, to decide what value, if any, shall be assigned to the 
non -protein. 

786. Early investigations. — Following the recognition of 
the fact that the substances grouped under the collective term 
non-protein make up a considerable share of the nitrogenous 
matter of numerous feeding stuffs, much labor has been ex- 
pended in efforts to determine their nutritive value as com- 
pared with that of the true proteins. These investigations 
have been summarized by the writer elsewhere. 1 While 
much diversity of opinion has prevailed, the general tendency 
has been to consider the non-protein as of questionable value. 
Kellner, the leading German authority, in particular, regarded 
it as valueless. 

787. New viewpoint. — With advancing knowledge of the 
chemistry of the proteins and of the chemical mechanism of 

1 Principles of Animal Nutrition, pp. 52-58 ; U. S. Dept. Agr., Bur. Anim. Indus., 
Bui. 139 (1911). 



THE PRODUCTION VALUES OF FEEDING STUFFS 685 

protein nutrition, however, it has become increasingly evident 
that many of these earlier results are of little real significance 
and that the question of the nutritive value of non-protein must 
be approached from a different standpoint. It has become 
evident, for example, that attempts to replace proteins com- 
pletely by a single amino acid or even by two or three of them 
must necessarily fail, since the formation of body protein re- 
quires the presence of all its constituent building stones in 
proper proportions. For the same reason the addition of an 
amino acid to a ration can be effective only if the proteins of 
that particular ration happen to be deficient in that one con- 
stituent. 

Furthermore, experiments with ingredients of the non-protein 
which do not form part of the protein molecule are of question- 
able significance. For example, asparagin, which has been a 
favorite subject of investigation for reasons of convenience, is 
not found among the cleavage products of the proteins but be- 
longs to the class of acid amides. So far as appears, it could 
contribute to the formation of protein only after conversion into 
the related aspartic acid (47) and it has not yet been shown 
that the body can undo the amide linkage of nitrogen. More- 
over, as appeared in Chapter I (60-67), the non-protein in- 
cludes, in addition to acid amides like asparagin, a great 
variety of nitrogenous substances which are but remotely re- 
lated chemically to the proteins and whose nutritive value is 
at best doubtful. 

It would appear that the value of the non-protein of a feeding 
stuff as a source of body protein must be determined by pre- 
cisely the same thing which is believed to measure the value of 
an individual protein or of the mixed proteins of feeding stuffs, 
viz., the kinds and proportions of amino acids which it can 
yield, since there is no evident reason why an amino acid ex- 
isting ready formed in a feeding stuff should differ in value from 
the same substance split off from protein in the process of di- 
gestion. If this be admitted, however, the distinction made in 
recent years between protein and non-protein in feeding stuffs 
becomes rather meaningless. If the value of each is measured by 
its amino acid content, then what is needed to fix the produc- 
tion values of feeding stuffs as regards protein is a knowledge of 
the kinds and amounts of these compounds which the feeding 



686 NUTRITION OF FARM ANIMALS 

stuff as a whole (i.e., its crude protein) can furnish, irrespective 
of whether they exist in a soluble, as it were predigested, form or 
are first produced in the digestive tract of the animal. 

788. Indirect utilization of non-protein by herbivora. — In 
the case of herbivora, especially of ruminants, another factor 
enters into the consideration of the value of the non-protein, 
viz., its relation to the ferment organisms which play so large 
a part in the digestive processes of these animals. 

It was stated in Chapter III (141) that the presence of soluble 
nitrogenous compounds in the feed tends to stimulate the mul- 
tiplication and activity of these organisms, thus bringing about 
an increase in the excretion of methane and in the proportion 
of carbohydrates apparently digested. It was likewise indicated 
that the protein produced at the expense of non-protein in the 
multiplication of the microorganisms might serve as a source of 
protein to the body and thus bring about an indirect utilization 
of the non-protein. Much experimental evidence supporting 
this view is on record, particularly the extensive investigations 
of Morgen and his associates, which have been discussed else- 
where l by the writer. Three general conclusions regarding 
the behavior of non-protein in the body were drawn, viz. : — 

In ruminants, a conversion of non-protein into protein appears 
to be effected by the microorganisms of the digestive tract. 
The extent of this conversion appears to be relatively greater 
in the case of ammonium salts and asparagin than in that of 
the non-protein of vegetable extracts. 

The protein thus formed from non-protein seems to be digested 
subsequently. The apparent formation of indigestible protein 
observed by some investigators appears to be due to an increase 
in the metabolic products contained in the feces, 'caused by the 
specific action of the vegetable extracts upon the digestive 
tract. 

By means of its conversion into bacterial protein, the non- 
protein in the feed of ruminants may serve indirectly for main- 
tenance and also as a source of protein for milk, and probably 
for growth, in rations deficient in protein. 

Quantitatively, however, the various forms of non-protein 
used in these experiments were much inferior to protein and a 
substitution of the former for the latter caused a marked falling 

1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 139 (1911). 



THE PRODUCTION VALUES OF FEEDING STUFFS 687 

off in production. For maintenance alone, non-protein seemed 
quite effective, but neither for growth nor for milk production 
could it equal protein. It seems probable that the limiting 
factor in this indirect utilization of non-protein is the extent to 
which it can be synthesized into protein by the microorganisms 
rather than any inferiority in the nutritive value of the result- 
ing protein. 

789. Conclusions. — It seems clear that the evidence is in- 
sufficient to warrant any general conclusions regarding the nu- 
tritive value of non-protein, if indeed any general statement 
regarding such a heterogeneous group is possible. Ultimately, 
it may be that studies of the amino acid yields of the total ni- 
trogenous matter (crude protein) of feeding stuffs, or com- 
parisons of its relative efficiency in supporting maintenance or 
growth, will lead to the formulation of production values for 
the crude proteins of different materials, but for the present 
the writer feels that the safer course is to make the digestible 
" true " protein, so-called, the basis of comparison. 

While some experiments, notably the Copenhagen experi- 
ments on dairy cows (586), seem to indicate a relatively high 
value for the non-protein of roots especially, most investigators, 
particularly Morgen and his associates, have, as already noted, 
found them decidedly inferior to protein. It is true that the 
non-protein contains amino acids which may at times be utilized 
indirectly by herbivora through the agency of the microor- 
ganisms of the digestive tract, but even this indirect utilization 
seems to be rather limited in extent in most instances. The 
conventional " true " protein, on the other hand, may be re- 
garded as representing approximately the real proteins of a 
feeding stuff and it would seem that these mixed proteins are 
likely to supply more nearly a balanced amino acid mixture in 
digestion than would result from the inclusion of the non-pro- 
tein. Investigations of the protein values of feeding stuffs 
should doubtless take account of whatever amino acids the 
non-protein supplies, i.e., they should relate to the crude pro- 
tein. With continued study of these relations, it may be hoped 
that greater clarity may be attained, but until that end is 
reached, the digestible " true " protein seems the safer basis 
for the formation of tables of the production values of feeding 
stuffs and for the computation of rations. Whatever error is 



688 NUTRITION OF FARM ANIMALS 

thus involved tends to make the protein content of the rations 
somewhat higher than if the crude protein were made the basis 
of the computation. It is, therefore, an error on the safe side, 
since a deficiency of protein may limit production while a sur- 
plus at worst simply tends to increase the cost of the ration, and 
the difference in the latter respect is seldom considerable. 



CHAPTER XVIII 
THE COMPUTATION OF RATIONS 

§ i. Feeding Standards 

790. Origin. — As the hay values described in Chapter XVI 
(700) gradually gave place to new methods of comparing the 
values of feeding stuffs based upon improved methods of chemi- 
cal analysis and upon investigations into the general laws of 
nutrition, an attempt naturally followed to express the nutritive 
requirements of animals in a similar manner instead of in terms 
of gross weight of feed or of hay values. Thus originated the 
feeding standards for different species of farm animals which 
later came to be popularly regarded more or less in the light of 
prescriptions or recipes for successful feeding. 

791. Early standards. — The earliest suggestion along this 
line seems to have originated with Haubner l about 1840. 
Lingethal, 1 in 1857, amplified the suggestion, but Grouven 2 in 
1858 was the first to formulate specifically * the requirements 
of farm animals, expressing them in . terms of dry matter, 
total protein, total fat (ether extract), and " carbohydrates " 
(total material soluble in acids and alkalies). In other words, 
the crude nutrients were the basis of Grouven's standards. 

Wolff took the next step in advance by making the digestible 
nutrients as determined by the methods of Henneberg and 
Stohmann (707-710) the basis for comparisons of feeding stuffs 
and for expressing feed requirements. His feeding standards 
were first published in 1864 in Mentzel and von Lengerke's 
Landwirtschaf tlicher Kalender and were also incorporated in his 
widely read book, Die landwirtschaftliche Futterungslehre, in 
1874. These standards attempted to formulate the amounts 
of digestible protein, carbohydrates and fats which should be 

1 Quoted by Grouven ; Kritische Darstellung aller Futterungs-Versuche. Kas- 
sel, 1863, p. 327. 

2 Vortrage iiber Agricultur-Chemie, 1858. 

2 Y 68q 



690 NUTRITION OF FARM ANIMALS 

contained in rations for various purposes in order to secure 
satisfactory results under average conditions. Thus, the 
Wolff standard for dairy cows was : — 

Feeding Standard for Milk Cows per Day and iooo Pounds Live 

Weight 

Total dry matter 24 pounds 

Digestible protein 2.4 pounds 

Digestible fat . . 0.4 pound 

Digestible carbohydrates 12.5 pounds 

Nutritive ratio 1 : 5-4 

This means that any mixture of suitable feeding stuffs 
from which a cow can digest 2.5 pounds of protein and 13 
pounds of non-nitrogenous nutrients per day will constitute a 
suitable ration and produce a good flow of milk. 

The Wolff standards were introduced into the United States 
a few years later through the writings of Johnson, Atwater 
and others, and by the writer's translation of Wolff's book, 1 
and found wide currency among students of stock feeding and 
with popular writers. 

792. Modifications of the Wolff standards. — That with the 
progress of investigation modifications should be made in 
standards formulated fifty years ago was to be expected. From 
1864 to 1896 Wolff's standards were published annually in 
Mentzel and von Lengerke's Kalender practically unchanged. 
From 1897 to 1906 they were continued under the charge of 
Lehmann, who introduced some additions and modifications, 
the principal ones being the subdivision of the standard for dairy 
cows according to milk yield and the distinction between meat 
and milk or wool breeds in the standards for growing animals. 
These constitute the well known Wolff -Lehmann standards. 

793. Kellner's standards. — Both the Wolff and the Wolff- 
Lehmann standards, as already noted, were expressed in terms 
of the so-called digestible nutrients. Kellner, in 1905, in the 
first edition of his Ernahrung der landwirtschaftlichen Nutz- 
tiere, proposed the system of calculation by means of starch 
values (772) which has since been associated with his name, 
and formulated a table of feeding standards expressed accord- 
ing to this new method. 

1 Manual of Cattle Feeding, 1880. 



THE COMPUTATION OF RATIONS 691 

In one respect Kellner's standards differ radically from pre- 
ceding ones and constitute a notable advance. While the earlier 
standards, like the earlier tables of feeding stuffs, assume di- 
gestible protein, carbohydrates and fats from different sources 
to be of substantially equal nutritive value, Kellner's figures 
take account of those differences in the values of nutrients as 
sources of energy which have been revealed by recent inves- 
tigations and express the needs of animals in this respect in 
what are, in fact, although not in form, net energy values. In 
addition, his standards regard only the true protein as of 
value and they reduce somewhat the very high requirements of 
fattening animals for protein as postulated by early authors. 
In other respects, however, they are on substantially the plan 
of the Wolff -Lehmann standards, i.e., they are in form pre- 
scriptions or recipes for rations for different purposes. 

§ 2. Feed Requirements 

794. Limitations of feeding standards. — From the outset it 
was necessary to guard against misconceptions arising from the 
very definite form in which the feeding standards were pre- 
sented. Their authors insisted from the first that they were in- 
tended as general guides and not as fixed rules to be rigidly ad- 
hered to. But the human mind craves a recipe and there has 
been a persistent tendency to substitute for the study of the 
principles of nutrition a series of exercises in applied arithmetic. 
Others again, perhaps misled by the name, have interpreted the 
feeding standards as representing a physiological demand of 
the animal ; — a sort of moral ideal in feeding, to be aimed 
at, but concerning which concessions have to be made to human 
fallibility and the pressure of circumstances. 

The difficulty inherent, more or less, in all forms of feeding 
standards, but especially in the earlier ones, is that they fail 
to take sufficient account of the fact that the feeding of farm 
animals is an economic problem. A manufacturer would not 
buy some average amount of raw material which might be re- 
garded as the norm for his business, irrespective of the capacity 
of his own factory or of the market for the finished product. 
When high prices prevailed he might find it profitable to han- 
dle a maximum amount of raw material and so to reduce the 



692 NUTRITION OF FARM ANIMALS 

percentage of his overhead costs, even at the risk of some loss 
of efficiency in the manufacturing process. In the contrary case, 
he might find it necessary to run considerably below his max- 
imum capacity in order to tide over a bad season. In somewhat 
similar fashion it is necessary for the stock feeder to adapt his 
rations to the economic conditions under which he works. While 
the animal cannot be handled like a machine in a factory, never- 
theless, as has appeared in previous chapters, it shows a large 
degree of flexibility in its requirements both quantitatively and 
qualitatively. No single fixed standard is either physiologically 
or economically necessary for productive feeding. 

795. The feeder's problem. — As the feeder looks at his 
animals, the problem which they present is a threefold one. 

First, he must furnish them with sufficient repair material 
and energy to keep the body machinery running, i.e., he must 
supply a maintenance ration. The requirements for this pur- 
pose, although subject to individual variations, have been 
worked out with some degree of accuracy and this part of his 
problem is relatively simple. 

Second, in addition to a maintenance ration, he must supply 
his animals with the amounts of matter and of energy necessary 
for the production of the meat, milk or work which he desires 
them to yield. Here his task is much less simple. 

It is evident in the first place, as has been emphasized in 
previous chapters, that the producing capacity of the animal 
is the prime factor in the problem. No argument is necessary 
to show that a cow producing thirty pounds of milk daily re- 
quires a greater addition to her maintenance ration than does 
one having a capacity of only fifteen pounds, or that a steer 
which can gain three pounds daily needs more surplus feed than 
one capable of making only one pound of gain. Good business 
economy demands that the better animal be given feed sufficient 
in amount and kind to permit its producing capacity to be 
fully utilized, thus reducing the relative cost of maintenance. 
On the other hand, it would be an obvious waste to give a 
mediocre or poor producer a ration adequate for two or three 
times the production of which it is capable. 

Third, the feeder, like the manufacturer, must adapt his prac- 
tice to market conditions. As prices of feeding stuffs fall and 
those of animal products rise, he will tend to feed more in- 



THE COMPUTATION OF RATIONS 693 

tensively, but here he encounters the law of diminishing re- 
turns. The dairy cow affords, perhaps, the most striking il- 
lustration of this. An increase in the quantity of her feed above 
a moderate ration may be expected to cause an increase in milk 
secretion but at the same time an increasing proportion of the 
extra feed will be diverted to fattening (606-610). Similarly, 
a rather small protein supply appears adequate to support mod- 
erate milk production but larger amounts seem to act as a stim- 
ulus to the activity of the milk glands and to increase the yield 
of milk (603), but presumably at a diminishing rate. The dairy- 
man's problem is to utilize these stimulating effects up to the 
point at which the increase in yield is offset by the added cost 
of the ration, and the solution of this problem requires ex- 
perience and good judgment and is one in which little aid can 
be afforded by feeding standards. 

What is so emphatically true of dairy feeding applies in 
greater or less degree to all forms of animal production. Even 
though there may be no decrease in the utilization of the 
feed in the strict physiological sense, diminished digestibility, 
stimulation of incidental bodily activity, or changing com- 
position of increase tend to make heavy rations or high 
protein rations relatively less effective than more moderate 
ones. 

What the feeder needs in order to meet this situation intel- 
ligently is not so much a fixed standard, or group of standards, as 
a knowledge of the amount and kind of feed required under 
various conditions for the manufacture of a unit of product — 
a pound of increase in live weight, for example, or a pound of 
milk of a given quality. To the extent to which this infor- 
mation is available he can, knowing his animals, proportion 
the feed to the capacity of each and thus go far toward securing 
the most efficient production. It appears desirable, therefore, 
to assume a somewhat different point of view from that which 
has largely prevailed in the past and to substitute for the con- 
ception of feeding standards the modified conception of feed 
requirements. 

796. Feed requirements. — Haecker 1 appears to have been 
the first to apply this idea to milk production and to formulate 
the feed requirements for the production of a pound of milk 
1 Minn. Expt. Sta., Bui. 79 (1903), pp. 104-107. 



694 NUTRITION OF FARM ANIMALS 

of different grades. As modified by his subsequent experiments, 
this statement of requirements * has become known as the 
Haecker standard, although, strictly speaking, it is not a 
standard in the older sense. The writer 2 subsequently pub- 
lished a tentative statement of the protein and energy require- 
ments per pound of milk containing four per cent of fat and 
illustrated the computation of rations on this basis, without, 
however, attempting similar estimates for other grades of 
milk. Later Woll and Humphrey, 3 Savage 4 and Eckles 5 
have adopted various forms of the same conception. Henry 
and Morrison 6 have included in their modified Wolff-Lehmann 
standards Haecker's requirements for milk production and 
also similar data, based on unpublished results by the same 
.experimenter, for growing fattening steers, and have also 
widened somewhat the range of the standards for other pur- 
poses and introduced minimum and maximum figures. 

On the other hand, however, all of the foregoing requirements 
and standards, with the exception of Eckles', are expressed in 
terms of digestible nutrients and are therefore open to the 
criticism of ignoring differences in the relative values of nu- 
trients from different sources. 

797. Requirements in terms of protein and energy. — 
The several chapters of Part III were devoted primarily to a 
consideration of the feed requirements of farm animals in 
terms of digestible protein and of net energy. In the case of 
maintenance, these requirements may be regarded as to a cer- 
tain degree fixed and capable of computation upon the basis 
of the size of the animal, being related either to its weight or 
to its body surface. In the case of productive feeding, on the 
contrary, the obvious method of comparison is that of feed 
(in excess of maintenance) with yield, and an attempt was 
therefore made to estimate the feed requirements per unit of 
product. The results of these estimates have been brought 
together in Tables I- VI of the Appendix, which include also for 
convenience estimates of the total requirements per day and 
head for normal growth at different weights and ages. 

1 Minn. Expt. Sta., Bui. 140, p. 56. 

8 U. S. Dept. Agr., Farmers' Bui. 346 (1909), pp. 19-25. 

3 Wis. Expt. Sta., Research Bui. 13. 4 N. Y. (Cornell) Expt. Sta., Bui. 323. 

6 Mo. Expt. Sta., Research Bui. 7. 6 Feeds and Feeding, 15th Ed., p. 669. 



THE COMPUTATION OF RATIONS 695 

That the requirements there tabulated resemble more or less 
the earlier feeding standards and share to some degree their 
limitations is undeniable and likewise unavoidable. No finite 
number of formulas, however accurate, can cover specifically 
all the various conditions of practice, and in particular it is 
scarcely possible for them to include any consideration of the 
financial aspects of the matter. The most that seems possible 
is, first, to formulate the average requirements under ordinary 
circumstances and then to indicate as definitely as present 
knowledge permits, as has been attempted in Chapters VII- 
XIV, the influence of various conditions in modifying these 
requirements. The difference between the older and newer 
formulas lies far more in the point of view than in the com- 
pleteness or exact numerical accuracy of the figures and neither 
can be utilized as infallible recipes which shall spare the user 
the trouble of observing and thinking. 

798. Defects of the tables. — That not a few of the estimates 
of feed requirements contained in the Tables of the Appendix 
rest on quite meager data is apparent from the discussions in 
Part III. This is particularly true of the requirements for 
growth, as will be evident from a study of Chapter XI. To a 
somewhat less degree the same is true of those for milk pro- 
duction, the energy requirements in particular being based on 
an hypothesis regarding the cause of the higher net energy 
values for milk production (593, 605) which has not yet been 
submitted to experimental test. 

The estimates of the protein requirements are particularly 
unsatisfactory for two reasons. 

In the first place, they virtually assume all proteins to be of 
equal value. That such is not the case has been repeatedly 
stated in previous pages, but it has also been shown that 
present knowledge of the constitution of the vegetable proteins 
and of the amino acid requirements of the body is insuffi- 
cient to serve as the basis of a more satisfactory system. 

In the second place, there has been very little systematic 
investigation of the minimum protein requirements of farm 
animals for different purposes or of the percentage of different 
proteins capable of utilization for the production of body pro- 
tein or of milk protein. The requirements given in the 
tables are, to a large extent, based on observations in practice, 



696 NUTRITION OF FARM ANIMALS 

and it is quite possible that they may, with safety, be con- 
siderably reduced in some instances. 

Furthermore, the tables of the Appendix include no esti- 
mates of the ash requirements. This is not because the 
latter are unimportant, for it is not improbable that they may 
at times be a controlling factor, but simply because study 
in this field has not progressed far enough to permit of their 
formulation. 

But while it has seemed desirable to emphasize here certain 
defects of the feeding requirements as formulated, as a pre- 
caution against their uncritical use, they are by no means to 
be rejected as worthless but are capable of affording valuable 
aid to the intelligent feeder. By their use he can get a general 
idea of the feed requirements of his animals and can compute 
rations which will approximately supply the requisite amounts 
of protein and energy. His ability as a feeder will be shown, 
first, in his power to estimate the conditions which will modify 
the feed requirements of his particular animals and cause his 
feeds to vary from the average, and second, in the skill with 
which he can interpret the daily results and modify his feeding 
in accordance with them. 

799. Dry matter. — The amount of dry matter which the 
ration contains must also be taken into consideration. The 
total volume of feed which an animal requires, although rather 
variable, has its limits. In computing rations the most con- 
venient indication of the bulk of the feeds is the percentage of 
dry matter shown in the first column of Tables VII, VIII and 
IX of the Appendix. In very general terms it may be said 
that a 1000-pound ruminant should be given from 20 to 30 
pounds of dry matter per day, 25 pounds being perhaps a 
fair average, while for the horse smaller amounts will be 
appropriate. 

An examination of the tables shows that concentrated feed- 
ing stuffs contain much more protein and energy in proportion 
to their dry matter than do the forage crops. Evidently, then, 
in heavy feeding, where the purpose is to give the animal all the 
feed possible, the ration should consist as largely as practicable 
of concentrated feeding stuffs, because only in that way can the 
required amount of nutriment be obtained without unduly in- 
creasing the bulk of the ration. In light feeding, on the contrary, 



THE COMPUTATION OF RATIONS 697 

roughage may predominate, because it is usually relatively 
cheaper and can supply the required amount of feed in a bulk 
which the' animal can consume. 



§ 3. Method of Computation 1 

The examples given on the following pages are intended simply 
as illustrations of the method of using the tables of the Appendix 
and not as model rations. Limitations of space forbid the 
multiplication of examples, but the reader who grasps the 
method will have no serious difficulty in applying it to his 
own conditions, while facility will be acquired with surprising 
rapidity by practice. It will be observed that the form of 
these tables and the methods of computation do not differ 
materially from those which have been used for many years in 
computing rations on the basis of " digestible nutrients," al- 
though the significance of some of the figures is different. It 
may be added that the digestible protein in the tables is true 
protein — that is, it does not include the non-protein. 
Consequently the percentages, as well as the amounts esti- 
mated in the rations on succeeding pages, are somewhat 
smaller than in the older tables. 

800. Total feed required. — A bunch of " feeders " 2 to 3 
years old, averaging 1000 pounds per head and in better than 
average condition are to be fattened on clover hay and corn- 
and-cob meal. Such cattle, if of good grade, should weigh 
1400 pounds each when ready for market and should not re- 
quire over 200 days to make the gain of 400 pounds. They 
should therefore make an average gain of 2 pounds per day. 

It may be estimated (Table III) that a gain of 1 pound live 
weight by animals of this grade will require about 3.5 Therms 
of net energy value in the feed ; for a daily gain of 2 pounds, 
therefore, the requirement would be 7 Therms. To this must be 
added the maintenance requirement, which will increase as the 
animals grow heavier. For the average weight of 1200 pounds 
it is sufficiently accurate to use the maintenance requirement 
computed (Table I) for 1250 pounds, viz., 7 Therms. This 

1 The contents of this section are reproduced by permission of the Honorable 
Secretary of Agriculture, from Bulletin No. 459 of the U. S. Department of Agri- 
culture, prepared by the writer. 



6g8 



NUTRITION OF FARM ANIMALS 



makes the total net energy requirement per day 14 Therms on 
the average of the whole feeding period. 

If we assume that 2 pounds of grain will be fed for each pound 
of hay, it is easy to compute from the figures in the last column 
of Table VII the amount of feed required to supply 14 Therms 
of net energy, as follows : — 

Therms 

In 100 pounds of average clover hay 38.68 

In 200 pounds of corn-and-cob meal 151.60 

In 300 pounds of feed . 190.28 

In 1 pound of feed 634 

To supply 14 Therms requires 14 4- 0.634 = 22.08 pounds 
of total feed, consisting of 7.36 pounds of clover hay and 14.72 
pounds of corn-and-cob meal, or, in round numbers, 7J pounds 
of hay and 15 pounds of meal. 

This, of course, represents the average ration for the whole 
feeding period. At the beginning the feed will naturally be 
lighter and consist to a larger extent of hay, while the amount 
of feed, and especially the proportion of grain, will be gradually 
increased until, toward the end of the feeding, the animals are 
consuming all the grain they will take, with only enough hay to 
insure the necessary bulk and proper digestion. Naturally, 
too, the form in which the corn is given will usually be varied 
in the course of the feeding. 

801. Improvement of a ration. — In the foregoing example 
it was assumed that the feeding stuffs to be used had been 
decided upon and attention was directed simply to the quantity 
required. Let us now take up the question from the other end 
and see whether a study of the ration may not yield some 
suggestion of possible improvement. 

According to Table VII, clover hay and corn-and-cob meal, 
respectively, contain in 100 pounds : — 



Clover hay . . . 
Corn-and-cob meal 



Total Dry 
Matter 



Pounds 

87.1 
89.6 



Digestible 
Protein 



Pounds 
4.9 

5-7 



Net 
Energy 
Value 



Therms 
38.68 

75.80 



THE COMPUTATION OF RATIONS 



699 



The 7J pounds of clover hay in the ration will evidently 
contain : — 

87.1 X 0.075 = 6.53 pounds of dry matter. 
4.9 X 0.075 = °-37 pound of digestible protein. 
38.68 X 0.075 = 2 -9° Therms of net energy value. 

A precisely similar computation for the corn-and-cob meal 
gives the following results : — 

89.6 X 0.15 = 13.44 pounds of dry matter. 

5.7 X 0.15 = 0.85 pound of digestible protein. 
75.8 X0.15 = 11.37 Therms of net energy. 

Adding these amounts, we find that the total ration contains : 



Clover hay, 7! pounds . . . 

Corn-and-cob meal, 15 pounds 

Total 



Total Dry 
Matter 


Digestible 
Protein 


Pounds 

6-53 
13-44 
19.97 


Pounds 
0-37 

1.22 



Net 
Energy 
Value 



Therms 

2.90 

n-37 

14.27 



The quantity of energy, of course, corresponds with that 
estimated to be necessary, because the amounts of feed were 
fixed upon on that basis. We observe, however, that the 
amount of digestible protein in the ration is less than that 
estimated in Table IV to be needed by beef cattle of this age 
and weight. A ration like the above might produce fair gains, 
but it probably would fail to take full advantage of the capac- 
ity of such cattle for growth and the gain would most likely 
fall below that which was anticipated. An increase in the pro- 
tein might be expected to make the ration more efficient. 

To make any marked change in the ration in this respect, it 
is evident that we must introduce into it some feed much richer 
in protein than either of those composing it. On consulting 
Table VII it is evident that what we need is one of the by-prod- 
uct feeds, like gluten feed or meal, the oil meals, etc., and also 
that only a small amount of one of these will be needed to effect 
a marked change in the ration. Thus, if we substitute 2 pounds 
of old-process linseed meal for 2 pounds of the corn-and-cob 
meal, the ration will foot up as follows : — 



700 



NUTRITION OF FARM ANIMALS 



Clover hay, i\ pounds .... 
Corn-and-cob meal, 13 pounds . 
Old-process linseed meal, 2 pounds 

Total 



Total Dry 
Matter 


Digestible 
Protein 


Pounds 

6-53 

II.65 

1.82 


Pounds 

0.37 
•74 
•57 

1.68 


20.00 



Net 
Energy 
Value 



Therms 
2.90 
9-85 
1.78 

14-53 



Thus at a comparatively small additional expense we are 
able to improve the ration materially by adding the lacking 
protein, and there is little doubt that the improved ration would 
produce a more rapid gain and, under ordinary conditions, a 
more profitable one as well, either by increasing the total gain 
or shortening the feeding period. 

802. Computing a ration from given feeding stuffs. — There 
are available for a dairy herd field-cured corn forage (including 
the ears), clover hay, corn meal, wheat bran and gluten feed. 
Table VII shows that these feeding stuffs, if of good average 
quality, will furnish in 100 pounds : — 



Corn forage 
Clover hay , 
Corn meal 
Wheat bran 
Gluten meal 



Total 

Dry 

Matter 


Digestible 
Protein 


Pounds 
81.7 
87.1 
88.7 
89.9 
90.9 


Pounds 

2-3 
4.9 

6.4 

" 10.8 

28.1 



Net 
Energy 
Value 



Therms 

43-94 
38.68 
85.20 
53-°o 
84.15 



The cows average 850 pounds per head and have produced in 
previous years an average of 20 pounds of milk per day testing 
4 per cent of fat. According to Table I, the maintenance 
requirement of such animals per day and head would be 
approximately : — 



Digestible protein 
Net energy . . 



0.43 pound 
5.40 Therms 



THE COMPUTATION OF RATIONS 



701 



For the production of 20 pounds of 4 per cent milk there would 
be needed, according to Table V : — 

Digestible protein (0.05 X 20) . . . . 1.0 pound 
Net energy (0.27 X 20) 5.4 Therms 

The total feed requirements per day and head are therefore : 



For maintenance 
For milk production 

Total . . . . 



Digestible 
Protein 



Pounds 

0.43 
I. OO 



1-43 



Net 
Energy 
Value 



Therms 
5 -4o 
5 -4o 



IO.80 



The problem, then, is to find a mixture of the available feed- 
ing stuffs which will yield these amounts of digestible protein 
and of energy, and which shall have a suitable bulk. 

The first step in the construction of a ration is to fix upon the 
amounts of coarse fodders. It is usually desirable to use as 
large a proportion of these as possible, since they are usually 
cheaper sources of feed than grain. On the other hand, the 
amount of them which an animal can consume is limited. Much 
depends upon the individual animals, and the proper amount 
can only be told by trial, but we should probably aim to get 
from 12 to 14 pounds of dry matter in the form of coarse fodder. 
Corn forage being a cheap feeding stuff, we shall naturally use 
this freely, with probably some hay for variety. By a little 
trial, we find that 10 pounds of corn forage and 6 pounds of clover 
hay will give us 13.4 pounds of dry matter and the amounts of 
digestible protein and of energy shown below : — 





Total 

Dry 

Matter 


Digestible 
Protein 


Net 
Energy 
Value 


Clover hay, 6 pounds 


Pounds 
8.17 
5-23 


Pounds 
0.23 
.29' 


Therms 

4-39 
2.32 


Total 


13.40 


•52 


6.71 







702 



NUTRITION OF FARM ANIMALS 



To this we have to add sufficient grain to bring the ration up 
to the requirement. The proper amount we must ascertain by 
trial. We will take, at a venture, 4 pounds of corn meal and 
2 pounds of wheat bran. Adding this to the ration we have : — 



Corn forage, 10 pounds 
Clover hay, 6 pounds 
Corn meal, 4 pounds 
Wheat bran, 2 pounds 
Total .... 



Total 

Dry 

Matter 


Digestible 
Protein 


Pounds 
8.17 
5- 2 3 
3-55 
1.80 


Pounds 

O.23 

.29 

.26 
.22 


18.75 


I. OO 



Net 
Energy 
Value 

Therms 

4-39 
2.32 

3-41 
1.06 

II. 18 



Comparing these totals with the requirement as computed, 
we rind that the ration is ample as regards energy, but consid- 
erably low in digestible protein. The rather low figure for dry 
matter shows that more feed may be added to the ration if 
desirable, but the total for net energy makes it evident that what 
is needed is not more feed, but feed of a different composition, 
supplying more protein along with rather less energy. Gluten 
meal answers this requirement, and substituting 2 pounds of 
it for 2 pounds of corn meal gives a ration which, while still a 
trifle high in energy, agrees as closely as necessary with the 
computed requirements. Thus : — 



Corn forage, 10 pounds 
Clover hay, 6 pounds 
Corn meal, 2 pounds 
Wheat bran, 2 pounds 
Gluten meal, 2 pounds 

Total .... 



Total 
Dry 

Matter 


Digestible 
Protein 


Pounds 


Pounds 


8.17 


0.23 


5-23 


.29 


1.77 


•13 


1.80 


.22 


1.82 


.56 


18.79 


1-43 



Net 
Energy 
Value 



Therms 

4-39 
2.32 
1.70 
1.06 
1.68 



11. 15 



This ration corresponds with the average requirement of the 
whole herd, since it is based on its average performance. It 
hardly need be said that it should be modified to suit the re- 
quirements and capacities of the individual cows, the heavy 
milkers getting more and the lighter ones less. 



THE COMPUTATION OF RATIONS 703 

By proceeding in this manner, with a little patience we can 
usually get a ration corresponding as closely as is necessary to 
the requirement, provided the feeds available admit of it. With 
a little experience one very soon learns to guess pretty closely, 
and with some practice the computations become very easy. 
An exact agreement with the requirement need not be sought 
for, since in practice the composition of the feeds will probably 
vary more or less from the average of the tables. 

803. The choice of feeding stuffs. — When, as in the last 
example, feeding stuffs must be purchased in order to get the 
desired relation between the protein and the energy of the 
ration, it is evident that often a wide range of choice may be 
offered. In such a case the question at once arises which of 
the various feeds available is it most economical to purchase, it 
being evident, of course, that this is not necessarily the one 
offered at the lowest price. 

No simple method of determining this point is possible, be- 
cause, as we have seen, the food serves two entirely distinct 
purposes in the body. Sometimes the supply of protein is the 
specially important point, and in other cases what is needed 
is a supply of energy without special reference to whether its 
source be protein or non-nitrogenous material. Consequently, 
the relative values of two feeding stuffs may vary under differ- 
ent circumstances. Some writers have based their compari- 
sons of the values of by-product feeds solely upon their con- 
tent of protein, for the reason that such feeds are often bought 
especially to supply this ingredient while the fats and es- 
pecially the carbohydrates are usually produced in abundance 
upon the farm. They regard that purchased feeding stuff as 
the most economical which furnishes a pound of digestible pro- 
tein at the lowest cost, ignoring any value in the other ingre- 
dients. It is obvious, however, that this is a one-sided view. 
The other ingredients have a value, and this is especially true 
in the case of a feeder who buys a considerable part of his grain 
supply and depends upon it as a source of energy as well as of 
protein. The method of comparison illustrated in the following 
pages is based primarily upon the cost per unit of energy because 
this is on the whole the most important function of the feed, 
but the method takes account also of the amount of protein 
present. 



7°4 



NUTRITION OF FARM ANIMALS 



Let us suppose the following feeding stuffs are available to 
a dairyman at the prices named : — 

Prices of feeds per ton 

Oats (40 cents per bushel) $25 

Corn meal 25 

Wheat bran 21 

Wheat middlings (flour) 24 

Dried brewers' grains 23 

Gluten meal . 27 

Cotton seed meal (prime) 30 

Old-process linseed meal 33 

The supply of coarse feed on the farm is sufficient to furnish 
each animal per day 32 pounds of silage and 8 pounds of clover 
hay ; the cows average 1000 pounds each and may be expected 
to produce per day about 24 pounds of milk testing 4.5 per cent 
fat. 

The first step is to compute, in precisely the same way as in the 
previous example, the estimated requirements of these cows 
per day as follows : — 



For maintenance . . 
For 24 pounds of milk : 

Protein 24 X 0.052 . 

Net energy 24 X 0.29 

Total requirement 



Digestible 
Protein 



Pounds 
0.50 

1.25 



i-75 



Net 
Energy 
Value 



Therms 
6.00 



6.96 



12.96 



The amount of silage and clover hay available will furnish, 
according to Table VII, the following amounts of dry matter, 
digestible protein, and net energy value : — 



Corn silage, 32 pounds 
Clover hay, 8 pounds 

Total 



Total 

Dry 

Matter 



Pounds 
8.42 
6.97 



iS-39 



Digestible 
Protein 



Pound 
0.19 

•39 



.58 



Net 

Energy 

Value 



Therms 
5-09 
3-09 



8.18 



THE COMPUTATION OF RATIONS 



705 



The question now is what feeding stuffs is it most economical 
to buy (or to refrain from selling if in stock) to complete the 
ration. The first step in deciding this question is to compare 
the various feeds as sources of energy and see which one fur- 
nishes a unit of net energy value at the lowest price. This 
computation gives the following results : — 



Oats 

Corn meal . . . ■ . . 

Wheat bran 

Wheat middlings . . . 
Dried brewers' grains 
Gluten meal . . . . 
Cottonseed meal . . . 
Old-process linseed meal 



Cost of 

100 
Pounds 


Energy 
Value of 

100 
Pounds 




Therms 


$1.25 


67.56 


1.25 


88.75 


1.05 


53-oo 


1.20 


75.02 


1.15 


53-38 


i-3S 


84.15 


1.50 


go. 00 


1.65 


88.91 



Cost of i 

Therm 

Net 

Energy 

Value 



Cents 

I.85 
I.41 
I.98 
1.60 
2.15 
1.60 
1.67 
1.86 



Evidently, if it were simply a question of supplying energy to 
the animals, we should use corn meal, since that supplies a unit 
of energy at a much lower price than any of the other feeding 
stuffs. If it were thought desirable to add variety to the ration, 
wheat middlings would obviously be our next choice. 

It is evident, however, without going through the labor of 
computation, that while corn meal and wheat middlings may 
be used in the ration, neither will supply enough protein if used 
exclusively. Of the available feeding stuffs which are rich 
in protein and which may therefore serve to balance the de- 
ficiency of this ingredient, gluten meal is relatively the cheapest, 
and cottonseed meal comes next. While the difference be- 
tween the two is not great, we shall naturally try the cheaper 
one. It is not difficult to determine by a few trials that 2§ 
pounds of corn meal and 3^ pounds of gluten meal, in addi- 
tion to the coarse fodder available, will give a ration corre- 
sponding very closely to the requirements, as the following 
table shows : — 



2 z 



706 



NUTRITION OF FARM ANIMALS 



Corn silage, 32 pounds 
Clover hay, 8 pounds 
Corn meal, 2§ pounds 
Gluten feed, 3! pounds 

Total .... 



Total 

Dry 

Matter 


Digestible 
Protein 


Pounds 


Pounds 


8.42 


O.19 


6.97 


•39 


2.22 


.16 


3.18 


•98 


20.79 


1.72 



Net 
Energy 
Value 



Therms 

5-09 
3-09 
2.13 

2-95 
13.26 



This ration shows as close an agreement with the computed 
protein requirement as could be desired, but contains a slight 
surplus of energy. The comparatively low figure for dry mat- 
ter indicates that more coarse fodder might have been used had 
it been available, with the probable effect of cheapening the 
ration. As it is, we have used the feeds relatively lowest in 
price and apparently have a very economical ration. 

Cottonseed meal, however, is nearly as cheap as a source of 
energy as gluten meal, while it contains considerably more pro- 
tein. It seems worth while, therefore, to see whether it may 
not be possible to secure the necessary protein more cheaply by 
using a smaller amount of the former feed in place of the gluten 
meal. Three pounds of cottonseed meal will supply almost 
exactly the same amount of protein as 3 J pounds of gluten meal. 
Making this substitution, the ration stands as follows : — 



Corn silage, 32 pounds . . 
Clover hay, 8 pounds . . 
Corn meal, 2\ pounds . . 
Cottonseed meal, 3 pounds 
Total 



Total 

Dry 

Matter 


Digestible 
Protein 


Pounds 
8.42 
6.97 
2.22 

2.77 

20.38 


Pounds 

0.19 

•39 
.16 

.96 

1.70 



Net 
Energy 
Value 



Therms 

5-09 
3-09 
2.13 
2.70 

13.01 



This ration agrees with the computed requirements even better 
than the previous one, while a simple comparison shows that it 
is a trifle cheaper. The grain portion of the two rations costs 
as follows: — 



THE COMPUTATION OF RATIONS 



707 



Corn meal . . 
Gluten meal . 
Cottonseed meal 

Total . . 



Second 
Ration 




It thus appears that the ration made up with the somewhat 
more expensive cottonseed meal is actually the cheaper. The 
difference, to be sure, is small, yet for 30 cows fed for 200 
days it would amount to $30. Such a difference is only likely 
to be found, however, when, as was assumed in this instance, 
some feed very high in protein can be had at a relatively cheap 
rate. In general, it may be said that when there are no very 
marked differences in the cost of a Therm of energy value in 
the feeding stuffs constituting the bulk of the ration, that one 
of the various high-protein feeds which supplies energy at the 
lowest cost should ordinarily be used, although it is always 
wise to check up this point, as in the example just given. 

804. The compounding of rations. — While in the foregoing 
examples an exact daily ration is computed, it would, of course, 
be utterly impracticable in most cases to weigh out separately 
each day's ration for each animal. Individual weighings of 
feeds at intervals would often yield valuable information and 
might profitably be undertaken, but for the ordinary routine 
of feeding, simpler methods must be used. 

When practicable, the grain feed may be advantageously 
mixed in advance in the desired proportions in as large quan- 
tities as the storage capacity available and the proper preserva- 
tion of the materials will permit. Where facilities are available, 
the whole amount of grain required for all the animals may be 
weighed out daily, or even for each feeding, without much ad- 
ditional labor. In distributing the grain to the individual 
animals, regard, of course, should be paid to their productive 
capacity and their individual peculiarities. The ration as 
computed is for the average animal. The skill of the feeder is 
shown in adapting it in quality and in amount to the individual. 



708 NUTRITION OF FARM ANIMALS 

Doubtless individual weighings at intervals, as already sug- 
gested, would be useful as a control on the accuracy of the 
distribution. 

The weighing of coarse fodder is usually a more difficult 
problem on account of its bulk. When, however, silage or cut 
fodder is handled in trucks, the matter is still comparatively 
simple. Long fodder, on the contrary, is not readily weighed. 
Nevertheless, even here an occasional weighing, if practicable, 
as a control upon the feeding, is very desirable. 

In all these and similar matters common sense is necessary. 
The computed ration expresses the best estimate that can be 
made of the actual average requirements, but it is at best more 
or less of an approximation. It would be foolish, therefore, to 
seek extreme exactness in realizing it or to go to more expense 
in the weighing and apportioning of the feed than the saving in 
the latter would amount to. The scale upon which the feeding 
is conducted will play an important part. Where scores or 
hundreds of animals are being fed, an exactness may profitably 
be sought which would be absurd in the case of two or three 
animals. Finally, it should be remembered that these com- 
puted rations are guides and not recipes. They may aid the 
feeder in wisely using the resources at his command, but they 
cannot take the place of experience and good judgment. 



APPENDIX 



APPENDIX 

ESTIMATED PROTEIN AND ENERGY REQUIREMENTS OF 

FARM ANIMALS 

Compare Chapter XVIII, § 2. 

Table I. — Maintenance Requirements of Cattle and Horses, Per 

Day and Head 



Live 
Weight 


Cattle 


Horses 


Digestible 
Protein 


Net Energy 


Digestible 
Protein 


Net Energy 


Metaboliz- 
able Energy 1 


Pounds 

150 

250 

500 

750 

1000 

1250 

1500 


Pounds 
O.08 
O.13 
O.25 
O.38 
O.50 
O.63 
0.75 


Therms 
1.69 
2.38 
3.78 

4-95 
6.00 
6.96 
7.86 


Pounds 
O.08 
O.13 
O.25 
O.38 
O.50 
O.63 
0.75 


Therms 
1. 16 
1.63 
2.58 

3-39 
4.10 
4.76 
5-37 


Therms 

3-36 

4.72 

7-50 

9.82 

11.90 

13.80 

15.59 



Table II. — Maintenance Requirements of Sheep and Swine, per 

• Day and Head 



Live 
Weight 


Sheep 


Swine 


Digestible Protein 


Net Energy 


Digestible Protein 


Net Energy 


Pounds 


Pounds 


Therms 


Pounds 


Therms 


20 


O.OII 


O.27 


O.OIO 


0.43 


40 
60 
80 


0.022 
0.033 
0.044 


0.43 
O.56 
0.68 


O.019 
0.029 
0.038 


O.68 
O.89 
1.08 


100 
120 


0.055 
0.066 


O.79 
O.89 


O.048 
O.058 


1.25 
I.41 


140 
160 
180 


0.077 
0.088 
0.099 


0.99 
1.09 
1. 17 


0.067 
0.077 
O.086 


1.56 
I.71 
I.85 


200 


O.IIO 


1.25 


O.096 


I.99 



1 To support heat production of animal at rest (387). 
711 



712 



APPENDIX 



Table III. — Requirements for Fattening with no Considerable 
. Growth — All Species — in Addition to the Maintenance 

Requirement 





Per Pound of Increase in 
Live Weight, in Addition 
to the Maintenance Re- 
quirement 


Digestible Protein 
per iooo lb. Live 
Weight, in Addi- 
tion to the Main- 
tenance Require- 




Digestible 
Protein 1 


Net Energy 




In early stages .... 
In late stages .... 
Average for entire fatten- 
ing period .... 


Pounds 

0.15 
O.05 

O.IO 


Therms 

2.50 
4.00 

3-25 . 


Pounds 
0.25-0.75 



Table IV. — Requirements for Growth with no Considerable 

Fattening 

a. Per Pound of Increase in Live Weight, in Addition to the Maintenance 

Requirement 



Age 


Cattle (and Sheep?) 


Swine 




Minimum of 
Digestible 
Protein 3 


Net Energy 


Minimum of 
Digestible 
Protein 3 


Net Energy 


Months 


Pounds 


Therms 


Pounds 


Therms 


o-l 


O.23 


1. 170 


O.17 


O.65 


1-2 


0.22 


I.272 


O.16 


O.77 


2-3 


0.22 


1-374 


O.15 


O.88 


3-6 


0.2I 


1.680 


O.14 


1.23 


6-9 


0.2I 


1.986 


O.I2 


1-59 


9-12 


O.20 


2.292 


O.IO 


1.96 


12-18 


O.18 


2.904 


0.07 


2.66 


18-24 


O.16 


3.000 


— 


— 


24-30 


O.14 


3-250 







1 Estimated from protein content of increase. 

2 Estimated from experiments on fattening (456). 

3 Estimated protein content of increase. 



APPENDIX 



713 



b. Per Day and Head, Including Maintenance 
(1) Cattle 





Beef Breeds 


Dairy Breeds 


Age 
















Live 


Digestible 


Net 


Live 


Digestible 


Net 




Weight 


Protein 1 


Energy 


Weight 


Protein l 


Energy 


Months 


Pounds 


Pounds 


Therms 


Pounds 


Pounds 


Therms 


1 


125 


0.70 


3-7 


100 


O.40 


3-1 


2 


175 


0.85 


4.2 


135 


0.45 


3-4 


3 


200 


0.90 


4.2 


165 


0.55 


3-6 


6 


350 


i-i5 


5-o 


275 


O.70 


4.1 


9 


450 


1.25 


5-7 


325 


0.75 


4.4 


12 


55o 


1.40 


6-5 


400 


O.80 


5-i 


18 


750 


1.40 


8.2 


55o 


0.85 


6.4 


24 


900 


1.30 


9-3 


700 


O.85 


7.6 


30 


1000 


1.30 


9.9 


800 


O.85 


8.2 



(2) Sheep 



. 


Wool Breeds 


Mutton Breeds 


Age 


Live 

Weight 


Digestible 
Protein x 


Net 

Energy 


Live 

Weight 


Digestible 
Protein l 


Net 
Energy 


Months 

3 

6 

9 
12 
18 


Pounds 

37 
65 
82 
90 
100 


Pounds 
0.13 
O.18 
O.17 
0.15 
0.12 


Therms 
0.78 

o-95 
1.06 
1. 12 
1. 19 


Pounds 
40 
72 
98 

US 
I50 


Pounds 
0.22 
O.30 
O.28 
O.25 
0.22 


Therms 
O.84 
1.03 
1.22 
I.36 
I.64 



(3) Swine 



Age 


Live Weight 


Digestible Protein 1 


Net Energy 


Months 


Pounds 


Pounds 


Therms 


1 


IS 


O.IO 


0.65 


2 


30 


0.20 


1. 00 


3 


52 


0.30 


1.38 


6 


Il8 


0.40 


2.28 


9 


183 


0.50 


3.06 


12 


250 


o.55 


3.80 



1 Based on Kellner's standards. 



7i4 



APPENDIX 



Table V. — Requirements for Milk Production 

Add to the maintenance requirement the following amounts for each 
pound of milk of the several grades. 



Grade of Milk 


Digestible Protein 


Net Energy 


Per Cent Fat 


Pounds 


Therms 


2-5 


0.041 


0.190 


3-o 


O.043 


0.214 


3-5 


0.045 


0.238 


4.0 


0.049 


0.265 


4-5 


0.052 


0.291 


5-o 


O.055 


0.3I5 


5-5 


0.058 


0.338 


6.0 


0.061 


0.361 


6-5 


0.064 


0.385 


7.0 


0.068 


0.408 



Table VI. — Requirements for Work Production by the Horse (674) 
Per 1000 Pounds Live Weight 



Full work — 8 hrs. per day . . 
Half work — 4 hrs. per day . . 
One-fourth work — 2 hrs. per day 



Digestible 
Protein l 



Pounds 
2.0 
1.4 
1.0 



Net Energy 2 



Therms 

18.2 

11. 1 

7.6 



AVERAGE DRY MATTER, DIGESTIBLE PROTEIN AND NET 
ENERGY VALUES OF FEEDING STUFFS PER 100 POUNDS 

Henry and Morrison 3 have recently published a very valu- 
able compilation of American analyses of feeding stuffs and of 
the results of American digestion experiments, and on this basis 
have calculated the content of digestible nutrients in a great 
variety of feeding stuffs. 

With the permission of these authors and with the cooperation 
of Assistant Professor Fred Silver Putney, of The Pennsylvania 
State College, the writer has computed from their tables the net 

1 Kellner's standards. 2 To be computed from Table VIII. 

3 Feeds and Feeding, 15th Edition, pp. 633-666. 



APPENDIX 



715 



energy values of the more important feeding stuffs in the man- 
ner described in Chapter XVII (773, 774) with the results re- 
garding ruminants reported in Bulletin No. 142 of the Pennsyl- 
vania Experiment Station and in Bulletin No. 459 of the U. S. 
Department of Agriculture. Those results, with a few addi- 
tions and corrections, are here reproduced and the computa- 
tion has also been extended, as well as the meager basis now 
available will permit, to the data regarding swine supplied by 
Henry and Morrison's tables. The figures for the horse are de- 
rived in part from the same source and in part from Zuntz 
and Hagemann's investigations, the net energy values being 
computed according to the method proposed by those investi- 
gators (775-778). The tables show primarily the net energy 
values for maintenance or fattening. There seems good reason 
for believing, however, that they may be taken without serious 
error to represent also the net energy values for growth and 
for work production and at least the relative values for milk 
production. 

Henry and Morrison's tables include only the crude protein 
(N X 6.25). The amount of non-protein has been estimated 
from the crude protein by the writers on the basis of Kellner's 
averages. 

Table VII. — Values per 100 Pounds for Ruminants 



Dried Roughage 

Hay and fodder from cereals 

Brome grass, smooth 

Corn (maize) fodder (ears included, medium 

dry) . 

Corn (maize) stover (ears removed, medium 

dry) . 

Kafir fodder, high in water 

Kafir stover, high in water 

Millet, Hungarian 

Mixed timothy and clover 

Oat hay 





Digestible 


Dry 

Matter 






Crude 
Protein 


True 
Protein 


Pounds 


Pounds 


Pounds 


Qi-5 


5-o 


3-5 


81.7 


3-o 


2-3 


81.0 


2.1 


1.6 


71.7 


3-o 


1.8 


72.7 


i-3 


1.0 


85.7 
87.8 


5-o 

5-3 


3-9 
3-6 


88.0 


4-5 


3-9 



Net 

Energy 

Value 



Therms 
40.83 

43-94 

31.62 
34.28 
27.65 
46.96 
40.85 
32.25 



716 



APPENDIX 



Table VII. — Values per ioo Pounds for Ruminants (Continued) 



Dried Roughage 

Hay and fodder from cereals 

Orchard grass 

Prairie hay 

Red top 

Sorghum fodder, computed to 80 per cent dry 

matter 

Timothy, all analyses 

Timothy, before bloom 

Timothy, early to full bloom 

Timothy, late bloom to early seed . . . . 
Timothy, nearly ripe 

Hay and fodder from legumes 

Alfalfa, all analyses 

Alfalfa, before bloom 

Alfalfa, in bloom 

Alfalfa, in seed 

Clover, alsike 

Clover, crimson 

Clover, red, all analyses 

Clover, red, before bloom 

Clover, red, in bloom 

Clover, red, after bloom 

Clover, sweet white 

Cowpeas, all analyses 

Cowpeas, before bloom ....... k . 

Cowpeas, in bloom to early pod ..... 

Soybeans 

Straws 

Barley 

Buckwheat 

Oat . . 

Rice 

Rye '.'.■'.'.'. 

Wheat 



Dry 

Matter 



Pounds 

88.4 

93-5 
90.2 

80.0 

88.4 
92.8 
87.2 
85-1 

87.5 



91.4 

93-8 

92.5 
89.6 

87.7 
89.4 
87.1 
89.6 
86.1 

77-9 
91.4 

90.3 
92.2 

89.4 
91.4 



85.8 
90.1 
88.5 
92.5 
92.9 
91.6 



Digestible 



Crude 
Protein 



Pounds 

4-7 
4.0 
4.6 

2-5 
3-0 

4-7 
3-6 
2.4 
2.2 



10.6 

154 
10.5 

8-5 
7-9 
9-7 
7.6 

11.6 
8.1 
6.8 

10.9 

i3-i 
17.8 
12.6 
11. 7 



0.9 

4.2 
1.0 
0.9 
0.7 
0.7 



True 
Protein 



Pounds 

3-3 
2.9 

3-9 

i-5 
2.2 
2.9 

2-5 
1.8 

1.8 



7-i 

10.3 

6.7 

6.2 

5-3 
6.9 
4.9 

5-4 
5-3 
4-5 
6.7 
9.2 
12.8 
9-5 



0.6 

3-2 
0.8 
0.4 
0.5 
o-3 



Net 
Energy 
Value 



Therms 

44-93 
40.42 
51.22 

32.20 
43.02 
43-52 
47.40 

37-54 
38.59 



34-23 
36-23 
32.33 
32.23 
34-42 
36.21 
38.68 
42.17 
39.12 

34-51 
38.98 
37-59 
33-54 
39-n 
44-03 



36.61 

4-55 
34.81 

23.63 

17-59 

7.22 



APPENDIX 717 

Table VII. — Values per 100 Pounds for Rumtnants {Continued) 



Fresh Green Roughage 
Green cereals, etc. 

Barley fodder 

Blue grass, Kentucky, before heading 
Blue grass, Kentucky, headed out 
Blue grass, Kentucky, after bloom 
Buckwheat, Japanese .... 

Cabbage 

Cabbage, waste outer leaves 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 

Corn (maize 



fodder, dent, all analyses 
fodder, dent, in tassel 
fodder, dent, in milk . 
fodder, dent, dough to glazing 
fodder, dent, kernels glazed 
fodder, dent, kernels ripe 
fodder, flint, all analyses 
fodder, flint, in tassel . . 
fodder, flint, in milk . . . 
fodder, flint, kernels glazed 
fodder, flint, kernels ripe 
fodder, sweet, before milk stage 
fodder, sweet, roasting ears or 



later 

Corn (maize) fodder, sweet, ears removed 

Millet, Hungarian 

Oat fodder 

Orchard grass 

Rape 

Rye fodder 

Sweet sorghum fodder 

Timothy, before bloom 

Timothy, in bloom 

Timothy, in seed 

Wheat fodder 



Green legumes 
Alfalfa, before bloom . . , 
Alfalfa, in bloom . . . . , 
Alfalfa, after bloom . . . , 

Clover, alsike 

Clover, crimson . . . . , 



Dry 
Matter 



Pounds 

23.2 
23.8 
36.4 
43-6 
36.6 
8.9 
14.1 
23.1 
14.9 
19.9 
25.1 
26.2 
34-8 
20.7 
10.6, 
15.0 
21.0 
27.9 
10.0 

20.3 
21.5 
27.6 
26.1 
29.2 
16.7 
21.3 
24.9 
24.2 
32.1 
46.4 
27.4 

19.9 

25-9 
29.8 

24-3 
17.4 



Digestible 



Crude 
Protein 



Pounds 

2-3 
3-7 
2.8 
1.9 
2.2 
1.9 

i-7 
1.0 
1.1 
1.0 

i-3 
1.1 

i-5 
1.0 
0.9 
0.9 
1.0 

1.2 

O.8 

1.2 
I.O 
1.9 

2-3 

i-7 
2.6 
2.1 
0.7 
1.8 
i-3 
i-5 
2.8 

3-5 
3-3 
2.1 

2-7 
2-3 



True 
Protein 



Pounds 

2.0 
2.8 
2.2 

1.6 
i-5 
i-3 
1.1 
0.8 
0.8 
0.8 
1.0 
0.8 
1.1 
0.8 
0.7 
0.7 
0.8 
0.9 
0.6 

0.9 
0.8 
1.1 
2.0 
1.1 
1-7 
1.4 
0.4 
1.1 
0.8 
1.0 
1.9 

1.9 
1.8 
i-3 
1-5 
1.6 



Net 
Energy 
Value 



Therms 

14.08 
14.82 
17.77 
21.01 
17.78 
8.87 

7-05 
14.60 

9-52 
13.64 

17-35 
16.74 
22.48 

13-53 
6.89 
10.39 
13-49 
17.84 
7.82 

13.38 
14.26 
17.24 
14.06 
15.81 
13-07 
15-99 
15-37 
18.36 
18.89 
26.36 
18.75 

9.20 
11.50 
11. 10 
14.56 
10.83 



718 APPENDIX 

Table VII. — Values per ioo Pounds for Ruminants {Continued) 



Fresh Green Roughage 
Green legumes 

Clover, red, all analyses . 

Clover, red, in bloom 

Clover, red, rowen 

Cowpeas 

Peas, Canada field 

Soybeans, all analyses 

Soybeans, in bloom 

Soybeans, in seed 

Vetch, hairy 

Silage 
Corn (maize), well-matured, recent analyses . 

Corn (maize), immature 

Corn (maize), from frosted ears 

Corn (maize), from field-cured stover . . . 

Clover 

Cowpeas 

Soybeans 

Sugar beet pulp 

Roots, Tubers, and Fruits 

Apples 

Beets, common 

Beets, sugar 

Carrots 

Mangels 

Potatoes 

Potato flakes 

Potato flour 

Pumpkins, field 

Rutabagas 

Turnips 

Grains 
Cereal grains 

Barley 

Buckwheat 

Corn (maize), dent 

Corn (maize), flint 

Corn (maize) and cob meal 



Dry 
Matter 



Pounds 

26.2 
27-5 
344 
16.3 
16.6 
23.6 
20.8 
24.2 
18.1 

26.3 
21.0 

25-3 
19.6 
27.8 
22.0 
27.1 
10.0 

18.2 
13.0 

16.4 

11. 7 

9.4 

21.2 

87.9 
89.4 

8-3 
10.9 

9-5 



90.7 
87.9 
89-5 
87.8 
89.6 



Digestible 



Crude 
Protein 



Pounds 

2-7 
2-7 
3-3 
2-3 
2.9 

3-2 
3-o 
3-i 
3-5 

1.1 
1.0 
1.2 
0.5 
i-3 
1.8 
2.6 
0.8 



0.4 
0.9 
1.2 
0.9 
0.8 
1.1 

3-6 
1.4 
1.1 
1.0 
1.0 



9.0 

8.1 
7.5 
7-7 
6.1 



True 
Protein 



Pounds 

1-7 
1.8 

2.2 

1-7 
2.1 
2.4 
2-3 
2-5 
2.4 

O.6 
O.4 
O.6 

0.3 
O.8 
I.I 
1-5 
0.5 

O.I 
O.I 

0.4 
0.5 

O.I 
O.I 

0.4 

0.1 

0.6 

0.3 

0.4 



8.3 

7.2 
7.0 
7.2 

5-7 



Net 
Energy 
Value 



Therms 

15-87 
16.74 
17.30 
10.42 
9.78 

12-53 
10.44 
12.70 
n-95 

15.90 
11.96 
14.27 
8.98 
7.26- 
11.05 

n-59 
9-32 



15-92 

7.84 

11.20 

9.21 

5-68 

18.27 

72.68 

80.09 

6.05 

8.46 

6.16 



89.94 

59-73 

85-5° 
84.00 

75.80 



APPENDIX 719 

Table VII. — Values per 100 Pounds for Ruminants (Continued) 



Net 

Energy 

Value 



Grains 
Cereal grains 

Corn (maize) meal 

Oats 

Oatmeal 

Rice, rough 

Rye 

Sorghum grain . . . 

Wheat, all analyses 

Wheat, winter 

Wheat, spring 

Leguminous seeds 

Beans, navy 

Cowpeas 

Peas, field 

Pea meal . 

Peanuts with hull 

Peanut kernel 

Soybeans 

Oil seeds 

Cottonseed 

Flaxseed 

Sunflower seed 

Sunflower seed with hulls 

Dairy Products 

Buttermilk . . . . 

Cow's milk 

Skim milk — centrifugal 

Skim milk — gravity 

Skim milk — dried 

Whey 

By-Products 
Fermentation industries 

Brewers' grains, dried 

Brewers' grains, dried, below 25 per cent 

protein 

Brewers' grains, wet 

Distillers' grains, dried, from corn .... 
Distillers' grains, dried, from rye .... 





Digestible 


Dry 

Matter 












Crude 


True 




Protein 


Protein 


Pounds 


Pounds 


Pounds 


88.7 


6.9 


6.4 


90.8 


9 


7 


8.7 


92.I 


12 


8 


n-5 


90.4 


4 


7 


4-5 


90.6 


9 


9 


9.0 


87.3 


7 


5 


6.7 


89.8 


9 


2 


8.1 


89.I 


8 


7 


7-7 


89.9 


9 


2 


8.1 


86.6 


18.8 


16.4 


88.4 


19.4 


16.9 


90.8 


19.0 


16.6 


89.1 


19.8 


17.2 


93-5 


19.4 


16.9 


94.0 


24.1 


22.2 


90.1 


30-7 


27-3 


90.6 


13-3 


11.9 


90.8 


20.6 


19.2 


95-5 


23-3 


20.2 


93- 1 


13-5 


n. 7 


9.4 


3-4 


3-4 


13.6 


3-3 


3-3 


9.9 


3-6 


3-6 


9.6 


3-i 


3- 1 


91.7 


34-4 


34-4 


6.6 


0.8 


0.8 


92.5 


21.5 


20.2 


91.8 


18.7 


17-5 


24.1 


4.6 


4.4 


93-4 


22.4 


18.3 


92.8 


13. 


6 


11. 1 



Therms 

85.20 
67.56 
86.20 
77-33 
93-71 
89-75 
91.82 
91.66 
91.41 

73-29 
79.46 
78.72 
77.62 

83-15 

109.04 

81.29 

78.33 
83-I7 
95-77 
92.49 

I3-32 
29.01 

I4-3 1 

15-43 

103.91 

10.39 



53.38 

50-93 
14-53 
85.08 
56.01 



720 APPENDIX 

Table VII. — Values per ioo Pounds for Ruminants (Continued) 



By-Products 
Fermentation industries 
Distillers' grains, wet .... 

Malt 

Malt sprouts 

Milling 

Buckwheat bran 

Buckwheat hulls 

Buckwheat middlings .... 

Hominy feed 

Red dog flour 

Rice bran, high grade .... 

Rice meal 

Rice polish 

Rye bran 

Wheat bran 

Wheat middlings, flour .... 
Wheat middlings, standard . . 

Oil extraction 
Cocoanut meal, low in fat . . . 
Cocoanut meal, high in fat . . 

Cottonseed hulls 

Cottonseed meal, choice . . . 
Cottonseed meal, prime . . . 
Germ oil meal, maize .... 
Linseed meal, new process . . . 
Linseed meal, old process . . . 

Palmnut cake 

Peanut cake from hulled nuts 
Peanut cake, hulls included . . 
Soybean meal, fat extracted . ,. 
Sunflower seed cake ..... 
Starch manufacture 

Gluten feed 

Gluten meal 

Starch feed, dry 

Starch feed, wet 

Sugar manufacture 

Molasses, beet 

Molasses, cane or black strap 





Digestible 




Dry 

Matter 






Net 


Crude 


True 


Energy 
Value 




Protein 


Protein 




Pounds 


Pounds 


Pounds 


Therms 


22.6 


3-3 


2.8 


22.05 


94.2 


15.8 


11.8 


87.82 


92.4 


20.3 


12.5 


72.72 


88.8 


10.5 


9.1 


30-59 


89.7 


0.4 


? 


-7.69 


88.0 


24.6 


20.8 


72.19 


89.9 


7.0 


6.5 


88.78 


88.9 


14.8 


13.2 


78.80 


89.9 


7-9 


7.0 


45-29 


90-5 


7-3 


6.4 


65.24 


90.0 


8.0 


7-i 


77.70 


88.6 


12.2 


10.5 


79-35 


89.9 


12.5 


10.8 


53-oo 


89-3 


15-7 


14.0 


75.02 


89.6 


13-4 


12.0 


59.10 


90.4 


18.8 


18.3 


83-49 


92.3 


18.4 


18.0 


100.31 


9°-3 


o-3 


? 


9.92 


92.5 


37-o 


35-4 


93-46 


92.2 


33-4 


32.0 


90.00 


91. 1 


16.5 


14.3 


83.88 


90.4 


3i-7 


30-9 


85.12 


90.9 


30.2 


28.5 


88.91 


89.6 


12.4 


12.0 


94.18 


89-3 


42.8 


41.4 


93-55 


94.4 


20.2 


i9.5 


42.57 


88.2 


38.1 


37-3 


99-65 


90.0 


32.0 


29.1 


88.87 


9i-3 


21.6 


20.1 


80.72 


90.9 


30.2 


28.1 


84.15 


90.7 


11. 2 


9.2 


77.46 


33-4 


4.1 


3-7 


30.45 


74-7 


1.1 


0.0 


57-IO 


74.2 


1.0 


0.0 


55-38 



APPENDIX 721 

Table VII. — Values per 100 Pounds for Ruminants (Continued) 



Net 
Energy 
Value 



By-Products 

Sugar manufacture 
Molasses beet pulp .... 
Sugar beet pulp, dried . . . 
Sugar beet pulp, ensiled . . 
Sugar beet pulp, wet . . . 
Packing house 

Dried blood 

Tankage 

Over 60 per cent protein 

55-60 per cent protein . . 

45-55 per cent protein . . 

Below 45 per cent protein . 





Digestible 


Dry 
Matter 






Crude 
Protein 


True 
Protein 


Pounds 


Pounds 


Pounds 


92.4 


5-9 


3-5 


91.8 


4.6 


0.7 


10.0 


0.8 


0.5 


9-3 


0.5 


o-5 


90-3 


69.1 


68.6 


92.6 


58.7 


55-6 


92.5 


54-o 


5i-i 


92.5 


48.1 


45-5 


93-5 


37-6 


35-6 



Therms 

76.28 

75-87 

9-32 

8.99 

68.12 

93-Q4 
83-58 
72.96 
54.16 



Table VIII. — Values per 100 Pounds for the Horse 



Alfalfa hay . . 
Red clover hay . 
Timothy hay . . 
Wheat straw . . 
Beans .... 
Corn (maize), dent 
Corn (maize), meal 

Oats 

Peas 

Linseed cake . . 
Carrots .... 
Potatoes . . . 





Digestible 


Dry 

Matter 






Crude 
Protein 


True 
Protein 


Pounds 


Pounds 


Pounds 


91.4 


10.9 


7-4 


87.1 
88.4 


7.2 

i.3(?) 


4-5 
o-5(?) 


91.6 


0.8 


0.4 


— 


19-5 


17.1 


89-5 
88.7 


5-9 
7-i 


5-4 

6.6 


90.8 
90.8 


9.9 
18.7 


8.9 
16.3 


90.9 


29-5 


27.8 


11. 7 


1.2 


0.8 


21.2 


1.9 


0.9 



Net 
Energy 
Values 



Therms 
48.82 

39-94 

26.64 

— 20.90 

109.40 

112.80 

132.70 

93-44 

105.20 

101.60 

16.60 

35-7Q 



3 A 



722 APPENDIX 

Table IX. — Values per ioo Pounds for Swine 



Grains 

Barley 

Corn (maize), dent 

Corn (maize) meal 

Corn (maize) and cob meal . . 

Pea meal 

Rice, rough 

Rye 

Sorghum seed 

JWheat 

Milling products 

Red dog flour 

Wheat bran 

Wheat middlings, standard . . 

Oil meals 
Linseed meal, old process . . 
Soybean meal 

Sundries 

Dried blood 

Tankage, over 60 per cent protein 

Potatoes 

Skim milk 





Digestible 


Dry 

Matter 






Crude 


True 




Protein 


Protein 


Pounds 


Pounds 


Pounds 


90.7 


8.8 


8.1 


89.5 


7.6 


7-i 


88.7 


7-i 


6.6 


89.6 


6.5 


6.1 


89.1 


21.4 


18.8 


90.4 


6-5 


6-3 


90.6 


9.9 


9.0 


87.3 


5-5 


4.7 


89.8 


9.9 


8.8 


88.9 


14.8 


13.2 


89.9 


12.0 


10.3 


89-5 


14.4 


12.7 


90.9 


28.8 


27.1 


88.2 


34.8 


34.o 


90-3 


59-2 


58.7 


92.6 


44.8 


41.7 


21.2 


1.8 


0.8 


9.9 


3-8 


3-8 



Net 
Energy 
Values 



Therms 
106.08 
118.82' 
120.25 
103.30 
122.43 
110.98 
123.68 
100.59 
108.85 



107.02 

74.95 

103.73 



110.85 
108.42 

116.89 

109.39 

24.69 

14.74 



APPENDIX 



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724 



APPENDIX 






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INDEX 



Abomasum, 80 

Accessory substances, 348, 421 

significance of, 632 
Acid: 

hippuric, 163 

hippuric, synthesis of, 163 
uric, synthesis of, 171 
Acidity in ash, significance of, 341 
Acidosis, 336 
Acids : 

excretion of, 338 
influence on digestibility, 627 
neutralization of, 337 
nucleic, 34 

anabolism, 168 
autogenesis, 169 
cleavages, 170 
deaminization, 171 
katabolism, 170 
metabolism, 168 
synthesis, 169 
organic, 40 
formation of, in digestion, 40, 158 
in feeding stuffs, 40 
metabolism of, 159 
Adipose tissue, 58, 424 

composition of, 59 
Age: 

best for fattening, 436 
influence on 

composition of gain, 431 
cost of production of meat, 430 
digestibility, 610 
effects of temperature, 454 
energy requirements for mainte- 
nance, 307 
feed consumption, 431 
net energy values, 666 
production of lean meat, 433 
relation of growth to, 373 
relation of protein requirements to, 
445 
Albuminoids, S3 
Albumins, 33 



Alfalfa proteins, value of, 683 
Alkali ratio of ash, 342 
Alkaloids, 37 
Amids, 37 

occurrence in plants, 38 
Amino acids, 37 

from simple proteins, 28, 29 

occurrence in plants, 38 

relative values for growth, 381 

required for maintenance, 314 
Ammonia, formation of, in katabolism of 

proteins, 165 
Amount of feed, influence on 

effects of temperature, 454 

meat production, 443, 449 

metabolizable energy, 664 

milk production, 515 

net energy values, 664 

production, 269 
of methane, 665 
Amylase, 78, 86 
Amylopsin, 78, 86 
Anabolism, 145 

of fats, 171 

nucleic acids, 168 
phosphorus, 180 
simple proteins, 160 
Animal : 

as factor in meat production, 428 
milk production, 470 

as prime motor, 192 
Araban, 15 
Arabinose, 9 
Arteries, 126 
Ascent, work of, 551 

efficiency of body in, 551 
Ash, s 

acid and basic, 340 

alkali ratio of, 342 

balance, 216 

maintenance of, 339, 344 

body, proportion of in bone, 48 
in offal, 56 

bone, composition of, 48 



725 



726 



INDEX 



Ash, — continued 
content of feed, 332 
correction of deficiencies in, 346 
determination of, in feeding stuffs, 67 
digestion of, 101 
effects of deficiency of, 420 
ingredients, 6 

availability of, 417 

balancing of, in ration, 343 

deficiencies in, 339 

digestibility of, 118, 333, 343 

excretion of, 141 

functions of, 187 

indispensable, 332 

metabolism of, 178 

skeleton as reserve of, 338 
losses of, 334 

causes of, 334 
of milk, 460 

sources of, 468 
outgo of, in milk, 520 
proportion of, in animal, 5 

in feeding stuffs, 5 
rate of storage of, in growth, 414 
requirements for growth, 414 

maintenance, 332 

milk production, 520 

work production, 562 
significance of acidity in, 341 
supply in dairy rations, 521 
total retention of, during growth, 
416 
Assimilative power : 

influence of breed on, 441 

individuality on, 441 
Autogenesis of nucleic acids, 169 

Balance : 
of ash, 216 
carbon, 205 

example of, 206 
energy, 216 

example of, 240 
income and expenditure, 194 
matter, 202 
nitrogen, 202 

determination of, 203 
example of, 203 
nutrition, 192, 201 

includes energy, 216 
water, 216 
Balance experiments, 200 

comparison with metabolism investi- 
gations, 241 . 
practical experiments, 244 



Balance experiments, — continued 

in agricultural investigations, 243 

significance of results of, 241 
Barley feed, 585 
Bases, organic, 37 
Bile, 86 
Blood, 123 

coagulation of, 125 

corpuscles, red, 124 
white, 124 

course of, 127 

plasma, 125 

platelets, 124 
Body: 

comparison with power plant, 567 

composition of entire, 61 
fat- and ash-free, 65 
fat-free, 64 

efficiency of. (See Efficiency) 

expenditure by, 192 

schematic, 195 

substances sources of energy for work, 

• 544 

temperature, chemical regulation of, 
263 
physical regulation of, 262 
Bone, 47 

ash composition of, 48 

composition of, 47 

proportion of body ash in, 48 
protein in, 48 
Bones as reserve of ash ingredients, 338 
Bran, 582 

rice, 583 

rye, 582 

wheat, 582 
Breakfast food residues, 584 
Breathing : 

mechanics of, 134 

regulation of rhythm of, 137 
Breed, influence on 

assimilative power, 441 

composition of milk, 473 

composition of milk solids, 474 

digestive power, 440, 610 

early maturity, 441 

feed consumption, 443 

maintenance requirements, 442 

meat production, 440 

net energy values, 666 
Brewers' grains, 586 
By-products, 582 

nature of, 582 
- of fermentation industries, 585 
milling, 582 



INDEX 



727 



By-products, — continued 
uses of, 584 
oil extraction, 586 

starch and glucose manufacture, 587 
sugar manufacture, 588 
the packing house, 590 

Calcium : 

metabolism of, 181 
occurrence of, 6 
Calorimeters, 221 
animal, 235 
emission, 236 
latent heat, 236 
respiration, 236 
water, 236 
Calves : 

energy requirements, 399 
gains by, in growth, 400 
protein requirements, 404 
Capillaries, 126 
Carbohydrates, 7 

cause of diminished digestibility of, 621 
classification of, 8 
digestible, 121 
digestion of, 89 

formation of fat from, 155, 174 
from fats, 178 
proteins, 167 
formed in the body, 155 
functions of, 186 

influence of excess of, on digestibility, 
616 
feeds rich in, on digestibility, 617 
katabolism of, 156 

intermediary, 157 
metabolism of, 152 
occurrence of, 7 
of milk, 460 

origin of, 467 
pentose, 9, 15 

metabolism of, 157 
relative utilization of fats and, for 
work production, 553 
Carbon balance, 205 

example of, 206 
Carbon dioxid : 
excretion of, 139 

determination of, 208 
through the skin, 139 
formed in respiration, 136 
product of metabolism, 144 
Carnivora, influence of feed consumption 

on heat production by, 657 
Cartilage, 49 



Cattle : 

energy requirements for growth, 339 
maintenance, 288 

influence of feed consumption on heat 
production, 651 

maintenance requirements of, com- 
pared with sheep, 294 

net energy values for, 659 
computation of, 667, 673 

protein requirements for growth, 404 
maintenance, 326 
Cell, 42 

enclosures, 45 

nucleus, 42 

structure, 42 

wall, 44 
Cellulose, 12 

digestion of, 89 

fermentation of, 90 
Cereal grains, 579 

composition and digestibility of, 580 

uses of, 581 

values of proteins of, 682 
Cerebrosids, 23 

Changes in digestion, summary of, 101 
Chemical changes in muscular contrac- 
tion, 532 
Chlorin, occurrence of, 7 
Choice of feeding stuffs, 703 
Cholesterins, 22 
Chymosin, 83 
Circulation, 123 

adjustment of, 131 

influence of work on, 535 

mechanics of, 128 

scheme of, 127 
Cleavage products, proportions of, in 

simple proteins, 31 
Coagulation of blood, 125 
Coarse fodders, 72, 572 

general character of, 572 

proportion of vegetative organs in, 576 
Ccecum, 84 
Collagens, 33 
Colloids, conversion of, into crystalloids 

in digestion, 102 
Colon, 85 
Combustible gases, outgo of chemical 

energy in, 230, 636 
Combustion, heat of, 223, 227 
Compounding of rations, 707 
Computation : 

of improvement of a ration, 698 
rations, 689 

from given feeding stuffs, 700 



728 



INDEX 



Computation, — continued 
method of, 697 
of total feed required, 697 
Concentrates, 72, 579 
comparison with roots, 579 

roughage, 662 
determination of digestibility of, 115 
proportion of, to roughage, 451, 696 
relative values for, 671 
Condiments, influence of, on digesti- 
bility, 627 
Condition, influence of, 
on economy of gain, 438 
meat production, 438 
rate of gain in fattening, 438 
Conditions affecting digestibility, 601, 

602, 613 
Conditions, external, influence of, on 
meat production, 453 
milk production, 478 
Conformation, relation of, to meat pro- 
duction, 443 
Conservation of energy, 219 
Contraction, muscular, 532 
chemical changes in, 532 
energy transformations in, 533 
Corn bran, 588 
Cottonseed meal, 587 
Critical temperature, 264, 453 

lowered by feed consumption, 308 
Crude fiber, 13 

composition of digested, 120 
correction of net energy values for, 

669 
determination of, in feeding stuffs, 71 
influence of, on heat production of 

horse, 676 
proportion oS pentosans in, 71 
Cutaneous excretion, outgo of chemical 

energy in, 231 
Cutting of roughage, influence of, on 

digestibility, 624 
Cytoplasm, 42 

Dairy rations : 

addition of fat to, 517 

ash in, 521 

protein in, 506 
Deaminization : 

of nucleic acids, 171 
simple proteins, 165 

reversible, 166 
Deficiencies in ash : 

correction of, 346 

effects of, 420 



Dextrins, 14 
Dextrose, 8 

Digestible nutrients. (See Nutrients) 
Digestibility, in, 601 
apparent, 120 

by horse compared with ruminants, 
604 

species of ruminants, 603 

swine compared with ruminants, 606 
conditions affecting, 601 
definition of, in 
determination of, in, 114 

influence of excretory products, 118 
influence on, 

of acids, 627 

addition of protein, 622 

age, 610 

breed, 610 

condiments, 627 

conditions relating to the animal, 602 
feed, 613 

cutting of roughage, 624 

drinking, 628 

drying, 623 

excess of carbohydrates, 616 

feeds rich in carbohydrates, 617 

grinding of grain, 624 

heavy feeding, 450 

individuality, 609 

non-protein, 622 

protein supply, 447 

quantity of feed, 613 

roots, 618 

species, 603 

tubers, 618 

water drinking, 628 

work, 610 
laboratory determination of, 116 
of ash ingredients, 118, 333, 343 

carbohydrates, diminished, cause of, 
621 

cereal grains, 580 

concentrates, determination of, 115 

ether extract, 119 

grasses, influence of maturity on, 

574 
maize forage, influence of maturity 

on, 575 
nitrogenous substances, 119 
protein, diminished, cause of, 619 
variable, 601 

variation of, at different times, 002 
Digestion, 77 
changes in, 101 
chemistry of, 89 



INDEX 



729 



Digestion, — continued 

conversion of colloids into crystal- 
loids in, 102 
experiments, example of, 114 
methods of, 112 
time required for, 113 
extent of protein cleavage in, 98 
intestinal, 87 

molecular simplification in, 103 
of ash, 101 

carbohydrates, 89 
cellulose, 89 
disaccharids, 95 
electrolytes, 101 
fats, 88, 95 
hemicelluloses, 92 
non-proteins, 96, 100 
nucleic acids, 99 
pentosans, 91 
phosphorus, 101 
proteins, 83, 88, 95 
by erepsin, 98 
pepsin, 96 
trypsin, 97 
starch, 79, 88, 92 
in intestines, 94 
stomach, 93 
sulphur, 101 
organs of, 77 

general plan of, 77 
solution of nutrients in, 10 1 
uniformity of nutritive material, 103 
work of, 277 

differences between feeding stuffs, 663 
roughage compared with concen- 
trates, 662 
Digestive power, influence of breed, 440 

individuality, 440 
Diminishing returns from feed in milk 

production, 515 
Disaccharids, 10 
digestion of, 95 
general properties of, 1 1 
Distillers' grains, 586 
Draft, work of, 552 

efficiency of body in, 552 
Dried blood, 590 
Drinking, influence of, on digestibility, 

628 
Dry matter, 3 

of body, composition of fat- and ash- 
free, 65 
requirements of, 695 
Drying, influence of, on digestibility, 623 
Duodenum, 84 



Economy of feeding, influence of indi- 
viduality on, 472 
Efficiency of body, 544 
as motor, 544 

compared with power plant, 567 
conditions affecting, 555 
economic, 562 
gross and net, 546 
in work of ascent, 551 

draft, 552 
influence on, 
of fatigue, 556 

forms of work, 555 
gait, 558 
grade, 559 
individuality, 556 
intensity of work, 557 
load, 559 
speed, 552, 557 
training, 556 
mechanical, 545 
over-all, 562 
per day, 549 
variable, 548, 555 
Efficiency of muscle, 545 
Electrolytes, digestion of, 101 
Embryo, net energy values for growth 

of, 393 
Emulsification of fats in digestion, 95 
Emulsion of fats, 19 
Energy : 

available, 233 
balance of, 216 
example of, 240 
in milk production, 493, 495 
chemical, 218 

outgo of, 229, 635 
conservation of, 219 
definition of, 216. 
expenditure in, 

internal work, measure of, 256 
feed consumption, 275 

significance of, 277 
locomotion, 550 

influence of speed on, 552, 557 
for work, body substance as source of, 

544 

protein as source of, 542 
forms of, 217 
gross, 227, 635 
income of, 226 
katabolism of, in fasting, 256 

constancy of, 256 
kinetic, 218 

measurement of, 325 



73Q 



INDEX 



Energy, — continued 
outgo of, 235 
losses of, 229, 235, 635 
chemical, 299, 635 
in feces, 230, 635 

fermentation, 230, 636 
computation of, 627 
heat production, 235, 650 
urine, 231, 636 
metabolizable, 231, 639 

comparison of net energy values 

with, 271 
computation of, 

from digestible nutrients, 646 
organic matter, 648 
factors for, 234 
for the horse, 675 
general conception of, 231 
influence on, of amount of feed, 664 
method of determining, 640 
of digestible nutrients, 648 

feeding stuffs, 642 
real and apparent, 645 
significance of, 645 
synonyms for, 233 
net. (See Net Energy) 
outgo of, 229, 235, 635, 650 
in combustible gases, 230, 636 
feces, 230, 635 
heat production, 235, 650 
urine, 231, 636 
production values as regards, 634 
protein as source of, 318 
rate of gain of, in growth, 378 
requirements 
for fattening, 361 
growth, 399 
of cattle, 399 
sheep, 401 
swine, 400 
maintenance, 267 
factors affecting, 304 
influence on 
of age, 307 
fattening, 306 
plane of nutrition, 305 
stage of fattening, 362 
temperature, 304 
manner of stating, 283 
methods of determining, 281 
modified conception of, 284 
of cattle, 288 
farm animals, 280, 303 
fowls, 301 
horses, 295 



Energy, — continued 
sheep, 292 
swine, 285 
relation of temperature to, 308 
meat production, 448 
milk production, 511 
work production, 562, 564 
sources of, for work, 542 
supply, influence of, on retention of 

protein, 386 
total, not measured by heat of com- 
bustion, 223 
transformations of, 218 

in muscular contraction, 533 
units, 220 
utilization of, 
in growth, 390 

milk production, 493 
work production, 544 
values, net. (See Net Energy Values) 
Environment, influence of, on milk 

production, 478 
Enzym reactions reversible, 150 
Enzyms as agents in metabolism, 148 
digestive, 78 
extracellular, 148 
intracellular, 149 
in the body, 150 
Epithelium, 105 
Erepsin, 79, 87, 98 

action of, on proteins, 98 
Esophagus, 79 
Ether extract : 
digested, 122 
digestibility of, 119 
of feeding stuffs, 70 
Excretion, 123, 139 

functions of kidneys in, 140 
of ash ingredients, 141 
carbon dioxid, 139 
nitrogenous products, 140 
water, 142 
Exercise : 

feed cost of, 481 

influence of, on meat production, 457 
milk production, 480 
yield of milk fat, 482 
Expenditure, balance of income and, 194 
of energy in horizontal locomotion, 
55o 
Extractives, percentage of, in lean meat, 

357 

Farm animals, composition of bodies of, 
62 



INDEX 



731 



Fasting : 

energy katabolism in, 251 
functions of protein in, 255 
katabolism, 249 
computation of, 282 
conditions affecting, 258 
energy expended in, 251, 257 
influence on, 
of body fat, 252 

external temperature, 262, 265 
muscular activity, 261 
previous feeding, 253 
size of animal, 258 
standing and lying, 262 
substances katabolized, in, 249 
protein katabolism in, 251 
normally small, 251 
variable, 251 
Fat and lean, proportions of in carcass, 

424 
Fat: 

addition of, to dairy rations, 517 
animal, sources of, 173 
body, influence of on fasting katabol- 
ism, 252 
proportion of in offal, 56 
computation of gain or loss of, 205 
crude, determination of, in feeding 

stuffs, 70 
gain or loss of, 205 
manufacture of, 172 
minimum of, for milk production, 519 
mobilization of reserve, 177 
of feed, resynthesis of, 171 
of milk, influence of exercise on yield 
of, 482 
origin of, 466 
percentage of, in lean meat, 356 
milk, influence of feed on, 528 
milk solids, influence of feed on, 529 
production, protein unnecessary for, 

363 
proportion of, in meat, 425 
relative utilization of carbohydrates 
and, for work production, 553 
requirements of, for milk production, 

5i6 
storage of, 172 
Fatigue, influence of, on efficiency of 
body, 556 
milk production, 482 
Fats, 16 

anabolism of, 171 

animal, elementary composition of, 21 

chemical changes in resorption of, 108 



Fats, — continued 

chemical reactions of, 18 
digestion of, 88, 95 
distinction between oils and, 19 
emulsification of, in digestion, 95 
emulsion of, 19 

formation of carbohydrates from, 178 
from carbohydrates, 155, 174 
protein, 168, 173 
functions of, 186 
hydrolysis of, 18 
katabolism of, 176 
melting points of, 19 
metabolism of, 171 
molecular structure of, 17 
native, 19 
occurrence of, 1 
of milk, 459 

oxidation of, at /3 carbon atom, 177 
physical properties of, 18 
relation of, to growth, 421 
saponification of, in digestion, 96 
specific effects of feeds associated with, 
527 
Fattening, 350 
best age for, 436 
composition of increase in, 350, 352, 

353,354-364 
concurrent, in milk production, 513 
contrast with growth, 396 
during growth, 448 
energy content of gain in, 361 
energy requirements for, 361, 448 
equivalent energy values for, 572 
gain of protein in, 354, 364 
influence of condition on, 438 
on composition of lean meat, 356 
energy requirements for mainte- 
nance, 306 
net energy values for, 360 
object of, 358, 427 
of mature animals, 35° 
pigs, protein requirements of, 41 1 
protein requirements for, 363, 446 
rations, protein in, 364 
requirements, 350, 359, 361, 363, 44°, 



stage of, influence of, on energy re- 
quirements, 362 
utilization of protein in, 364 
Fatty acids, 17 
Feces, 105, 109 

as excretory product, 109 

feed residue, 109 
composition of, 11 1 



732 



INDEX 



Feces, — continued 
losses of energy in, 635 
outgo of energy in, 230 
Feed: 

as stimulus to milk production, 522 
consumption, 

energy expended in, 275 
increases heat production, 273 
influence of, 

on heat production, 651 

by the horse, 675 
on metabolism, 651 
influence on, 
of age, 431 
breed, 443 
individuality, 443 
significance of energy expenditure in, 
277 
diminishing returns from, in milk 

production, 515 
dual function of, 183 
influence of, on composition of milk, 

527 
quantity of, influence of, on digesti- 
bility, 613 
requirements, 691, 693, 694 
for growth, 396 

maintenance, 280, 313 
meat production, 445 
milk production, 500 
supply, 569 

two aspects of, 631 
surplus, disposal of, 350 
total amount of, for meat production, 

449 
unit system, logical basis of, 595 
units, 593 

comparison of, with net energy 
values, 596 
utilization of, in milk production, 488 
Feeding as related to individuality, 444 
Feeding standards, 689 
early, 689 
for meat production, 451 

the horse, 566 
Kellner's, 690 
limitations of, 691 
origin of, 689 
Wolff's, 689 

modifications of, 690 
Feeding stuffs, 571 

accessory ingredients of, 632 

significance of, 632 
choice of, 703 
classes of, 72 



Feeding stuffs, — continued 
classification of, 571 
composition of, 66 
determination of 
ash in, 67 
crude fat in, 70, 71 
crude protein in, 68 
nitrogen-free extract in, 71 
non-protein in, 69 
protein in, 67 
true protein in, 67 , 

water in, 67 
direct comparisons of, 591 
ether extract of, 70 
metabolizable energy of, 639, 642 
production values of, 630, 634, 678 
relative values of, 591, 597 
rich in carbohydrates, influence of, on 

digestibility, 617 
specific effects of, 448 
associated with fats, 527 
on milk production, 523 
sources of, 571 
sundry ingredients of, 39 
Feeding trials, practical, 592 
Fermentation industries, by-products of, 

S85 
Fermentation, losses of chemical energy 
in, 636, 639 
computation of, 637 
Flavoring substances, 41 

influence of, on milk production, 522 
Fluids, digestive, 78 
Forms of work, influence of, on efficiency 

of body, 555 
Fowls : 

digestibility by, compared with swine, 

608 
energy requirements for maintenance 
of, 301 
Fruits, 579 
Fuel value, 283 
Functions : 

of ash ingredients, 187, 190 
carbohydrates, 186 
fats, 186 
feed, dual, 183 

non-nitrogenous nutrients, 187 
nutrients, 182 

physiological, 597 
proteins, 185 
water, 190 

Gain in fattening, energy content of, 
361 



INDEX 



733 



Gain in growth, energy content of, 

373 

rate of, in fattening, influence of con- 
dition, 438 
Gait, influence of, on efficiency of body, 

558 
Galactans, 14 
Galactolipins, 23 
Galactose, 9 
Gaseous exchange increased by work, 540 

through the skin, 139 
Gastric juice, 82 
Gelatinoids, 33 
Germ meal, 588 
Glands : 

parotid, 79 

salivary, 79 

sublingual, 79 

submaxillary, 79 
Globulins, 33 
Glucose manufacture, by-products of, 

587 
Glucosids, 10 

nitrogenous, 37 
Glutelins, 33 
Gluten feed, 588 

meal, 588 
Glycogen, 14 

computation of gain or loss of, 207 

content of body, 61 

conversion of, to dextrose in the liver, 

153 
formation of, in liver, 153 
gain or loss of, 205 
muscle, 154 
storage, 61 
Glycoproteins, 35 
Grade, influence of, on efficiency of 

^ body, 559 
Grain, influence of grinding on digesti- 
bility of, 624 
Grasses, 573 
influence of maturity on composition 

of, 573 
digestibility of, 574 
Grinding of grain, influence of, on diges- 
tibility, 624 
Gross energy, 635 
Group system, 477 - 
Growth, 371 

ash requirements for, 414 
contrast with fattening, 396 
energy requirements for, 399 
fattening during, 448 
feed requirements for, 396 



Growth, — continued 
increase in, 371 

composition of, 371 
involves storage of ash, 414 
measure of, 375 
minimum of protein for, 446 
nature of, 371 
net energy values for, 390 
of cattle, energy requirements for, 399 
protein requirements for, 404 
sheep, energy requirements for, 401 

protein requirements for, 407 
swine, effect of insufficient protein 
on, 409 
energy requirements for, 400 
protein requirements for, 408 
protein requirements for, 403 

results in practice, 403 
rate of, 373 

at different ages, 374 
rate of gain of energy in, 378 
protein in, 375 
storage of ash in, 414 
relation of fats to, 421 
relation of, to age, 373 
relative values of amino acids for, 381 

proteins for, 381 
retention of ash during, 416 
retention of protein in, 382 
influence of energy supply on, 386 
protein supply on, 384 
substances, 41, 348, 422 
total increase in, at different ages, 397 
utilization of energy in, 390 
feed in, 381 

protein in, 384, 387, 388 
Gums, 15 

Haemoglobin, 135 
Haemoglobins, 35 
Hay values, 591 
Heart, 125 

Heat energy, measurement of, 221 
unique, 220 
of combustion, 223, 228 
outgo of, 235 

production, causes of increase in, 275 
increased by feed consumption, 273 
influence on, of amount of feed, 665 
crude fiber, 676 
feed consumption, 651 

by the horse, 675 
roughage compared with con- 
centrates, 662 
losses of energy in, 650 



734 



INDEX 



Heavy feeding, influence of, on digesti- 
bility, 450 
net energy values, 450 
profitable in meat production, 449 
Hemicelluloses, 13 
digestion of, 92 
Hexosans, 12 
Hexoses, 8 
Hominy feed, 585 
Horse : 

computation of net energy values for, 

675, 676, 677 
digestibility by, compared with rumi- 
nants, 604 
energy requirements for maintenance 

of, 295 
feeding standards for, 566 
influence of feed consumption on heat 

production by, 675 
metabolizable energy for, 675 
protein requirements of, for mainte- 
nance, 329 
Humidity, influence of, on effects of 

temperature, 455 
Hydrolysis of simple proteins, 164 
Hydrogen, losses of energy in, 639 

Ileum, 84 

Improvement of a ration, computation 

of, 698 
Income, balance of expenditure and, 194 

of energy, 226 
Increase : 

composition of, 198 

influence of age on, 431 

in fattening, 

composition of, 350, 352, 353, 

354, 364 
energy content of, 352 
protein in, 364 
growth, 

composition of, 371 
energy content of, 373 
total at different ages, 397 
Individuality : 

feeding as related to, 444 
influence of 

on assimilative power, 441 
course of lactation, 473 
digestibility, 609 
digestive power, 441 
economy of feeding, 472 
efficiency of body, 556 
feed consumption, 443 
maintenance requirements, 442 



Individuality. — continued 

meat production, 440 

milk production, 514 

net energy values, 666 

yield of milk, 471 
Ingredients of milk, sources of, 465 
Initial and final states, law of, 223 
Intensity of work, influence of, on effi- 
ciency of body, 557 
Intercellular substance, 46 
Intestine, large, 85 

small, 84 
Inulin, 14 
Invertases, 79, 78 
Investigation, methods of, 194 
of details of metabolism, 194 
Ionic concentration, maintenance of, 188 
Iron, metabolism of, 181 

occurrence of, 6 
Isolation, shelter from, 457 

Jejunum, 84 
Juice, intestinal, 87 
pancreatic, 86 

Katabolism, 145 

computation of per unit of surface, 258 

to standard weights, 250 
fasting, 249 

conditions affecting, 258 
computation of, 282 
influence on, 
of body fat, 252 

external temperature, 262, 265 
muscular activity, 261 
previous feeding, 253 
size of animal, 258 
standing and lying, 261 
of protein variable, 251 
substances katabolized in, 249 
of carbohydrates, 156 
intermediary, 157 
energy in fasting, 251 

constancy of, 255 
fats, 176 
non-nitrogenous matter, influence of 

work on, 540 
nucleic acids, 170 
phosphorus, 180 
proteins, 162 

formation of ammonia in, 165 
nitrogenous end products of, 162 
two stages of, 164 
sulphur, 179 
products of incomplete, 230 



INDEX 



735 



Katabolism, — continued 
protein, 

dependent on supply, 322 
in fasting, 251 

normally small, 251 
influence on, of feed supply, 316 

work, 536 
in work, influence of non-nitrogenous 
nutrients on, 538 
stimulation of, in milk production, 515 
Keratins, 33. 57 
Kidneys, functions of, 140 
Kind of production, influence of, on net 

energy values, 666 
Kinetic energy, 218 
measurement of, 225 
outgo of, 235 

Lactase, 79, 87 
Lactation : 

course of, influence of individuality on, 

473 
stage of, bearing on experimental 

methods, 476 
influence on composition of milk, 476 
milk production, 476 
yield of milk, 476 
Lactose, n 

origin of, 467 
Lean meat, 424 

influence of age on production of, 433 

fattening on composition of, 356 
percentage of extractives in, 357 
fat in, 356 
Lecithins, 22 
Lecithoproteins, 35 
Legumes, 577 
Leguminous grains, 581 
Levulose, 9 
Ligament, 49 
Lignin, 13 
Linseed meal, 587 
Lipases, 79, 86 
Lipoids, 16 

cell, formation of, 172 
nitrogenous, 37 
Live weight as measure of nutritive 
effect, 196 
fluctuations of, 197 
influence of, on effects of temperature, 

454 
Liver, 86 

glycogenic function of, 152 
Load, influence of, on efficiency of body, 

559 



Locomotion, energy expenditure in, 550 
influence of speed, 552, 557 

Magnesium, metabolism of, 181 

occurrence of, 6 
Maintenance, 267 
amino acids required for, 314 
ash requirements for, 332 
definition of, 267 

energy requirements for, 267, 280, 303 
factors affecting, 304 
influence on 
of age, 307 
fattening, 306 
plane of nutrition, 305 
temperament, 304 
manner of stating, 283 
method of determining, 281 
modified conception of, 284 
relation of temperature to, 308 
matter requirements for, 313 
minimum of protein for, 

316, 323 
net energy values for, 271 
of ash balance, 339, 344 

cattle, energy requirements for, 288 

protein requirements for, 326 
fowls, energy requirements for, 301 
horses, energy requirements for, 295 

protein requirements for, 329 
neutrality, 335 
osmotic pressure, 335 
sheep, energy requirements for, 292 

protein requirements for, 327 
swine, energy requirements for, 285 
protein requirements for, 329 
optimum of protein for, 323 
protein requirements for, 313, 323 

nature of, 313 
relative values of proteins for, 315 
requirements, 269 
influence of breed, 442 
individuality, 442 
significance of, in interpretation of 
feeding experiments, 268 
in practice, 268 
true and live weight, 280 
value of non-protein for, 324 
Maize, influence of on metabolism, 664 

proteins, low value of, 681 
Maize forage, 575 
influence of maturity on composition 
of, 575 
digestibility of, 575 
Malt sprouts, 585 



736 



INDEX 



Maltase, 79, 87 
Maltose, 11 
Manifolds, 80 
Mannose, 9 
Matter : 

balance of, 202 
dry, 3 

requirements of, 
for fattening, 363 
growth, 403, 414 
meat production, 445 
milk production, 501, 520 
work production, 560 
Maturity : 

definition of, 428 
early, 428 

economic significance of, 429 
influence of breed on, 444 
influence of, 

on composition of grasses, 573 
maize forage, 575 
digestibility of grasses, 574 
maize forage, 575 
Meat, definition of, 424 
fat-free, composition of, 52 
proportion of fat in, 425 
Meat production, 424 
animal as factor in, 428 
combined growth and fattening in, 448 
energy requirements for, 448 
factors of, 427 
feed requirements for, 445 
feeding for, 444 
feeding standards for, 451 
heavy feeding profitable in, 449 
influence on, 
of age, 430 
condition, 438 
drinking water, 455 
exercise, 457 
external conditions, 453 
shelter, 456 
temperature, 453 
nature of, 424 
processes involved in, 426 
protein requirements for, 445 
relation of conformation to, 443 

type to, 443 
total amount of feed for, 449 
Metabolism, 144 

a gradual process, 147 
analytic, 146 
definition of, 144 
enzyms as agents in, 148 
general conception of, 144 



Metabolism, — continued 
general scheme of, 182 
influence on, of feed consumption, 651 
investigations, comparison of, with 
balance experiments, 241 
of details of, 194 
of ash ingredients, 178 
calcium, 181 
carbohydrates, 152 
fats, 171 
iron, 181 
magnesium, 181 
nucleic acids, 168 
nucleoproteins, 168 
organic acids, 159 
pentosans, 158 
pentose carbohydrates, 157 
phosphorus, 180 
potassium, 181 
. proteins, 160 
sodium, 181 
sulphur, 179 
oxidative, 146 
Metabolizable energy. (See Energy) 
Metaproteins, 35 

Methane, heat of combustion of, 636 
influence of amount of feed on pro- 
duction of, 665 
losses of energy in, 637, 639 
production of, in digestion, 90, 94 
Methods of investigation, 194 
Middlings, buckwheat, 583 

wheat, 583 
Milk: 
ash, 460 

sources of, 468 
average composition of, 461 
carbohydrates, 460 

origin of, 467 
components of, 459 
composition of, 461 
influence on, 
of breed, 473 

completeness of milking, 480 
feed, 527 

frequency of milking, 479 
stage of lactation, 476 
variability in same animal, 475 
energy content of, 511 
fat, influence of exercise on yield of, 

482 
fats, 459 

origin of, 466 
glands, 462 

development of, 463 



INDEX 



737 



Milk, — continued 

protein as stimulus to, 502 
influence of feed on percentage of fat 

in, 528 
proteins, 459 

origin of, 465 
secretion of, 464 

solids, composition of, influence of 
breed on, 474 % 
influence of feed on percentage of 

fat in, 529 
rate of production of, 469 
sources of ingredients of, 465 
yield of, influence on 

of completeness of milking, 480 
frequency of milking, 478 
individuality, 471 
stage of lactation, 476 
Milk production, 459 
a periodic function, 476 
animal as a factor in, 470 
ash requirements for, 520 
character of, 468 
concurrent fattening in, 513 
diminishing returns from feed in, 515 
energy balances in, 493, 495 
energy requirements for, 511 
factors of, 469 
fat requirements for, 516 
feed as stimulus to, 522 
feeding a secondary factor in, 500 
feeding for, 500 
influence on, 

of environment, 478 
exercise, 480 
fatigue, 482 

flavoring substances, 522 
frequency of milking, 478 
individuality, 514 
plane of nutrition, 514 
protein-rich feeds, 506 
protein supply, 504, 507 
shelter, 484 
stage of lactation, 476 
temperature, 483 

modifying factors, 484 
minimum of fat for, 519 

protein for, 501 
net energy values for, 493, 497 

equivalent fattening values, 498 
outgo of ash in, 520 
physiology of, 459 
protein as stimulus to, 502 

requirements for, 501 
relative values of proteins for, 492 



Milk production, — continued 
requirements for, 501 
specific effects of feed on, 523 
stimulation of katabolism in, 515 
supply of ash in, 521 
utilization of, 
energy in, 493 
feed in, 488 
protein in, 488 

estimate of, 489, 491 
Milking, completeness of, influence of on 
composition, 480 
yield, 480 
frequency of, influence of on composi- 
tion, 479 
yield, 478 
Milling, by-products of, 582 

uses of, 584 
Mineral matter, 5 
Molasses, 589 
Molasses feeds, 589 

Molecular simplification in digestion, 103 
Monosaccharids, 8 
composition of, 8 
Motion, tissues of, 50 
Motor, efficiency of body as, 544 
Mouth, 79 
Muscle extractives, 37 

fat-free, composition of, 52 
mechanical efficiency of, 545 
Muscles, 50, 531 
composition of, 51 
structure of, 50 
Muscular work, nature of, 531 

Net energy below critical temperature, 

310 
Net energy values, 271, 278, 634, 659 
comparison of feed units with, 596 

with metabolizable. energy, 272 
computation of, 667, 673, 677 
for the horse, 675, 676, 677 
from digestible nutrients, 667 

organic matter, 673 
independent of chemical composi- 
tion, 673 
importance of, 667 
correction of, for crude fiber, 669 
determination of, 272 
for cattle, 659 

different purposes, 279 
fattening, 360 
growth, 390 
of embryo, 393 
older animals, 393 



738 



INDEX 



Net energy values, — continued 
suckling animals, 391 
maintenance, 271 
milk production, 494, 497 

equivalent fattening values, 498 
ruminants, 660 
swine, 661 

work production, 563 
influence on, 
of age, 666 

amount of feed, 664 
breed, 666 
heavy feeding, 450 
individuality, 666 
kind of production, 666 
method of determination, 271 
of digestible nutrients, 668 
relative, for maintenance and fatten- 
ing, 361 
Neutrality, maintenance of, 189, 335 
Nitrogen balance, 202 
determination of, 203 
example of, 203 
Nitrogen factors, 69 
Nitrogen-free extract : 

composition of digested, .121 
constituents of, 72 

determination of, in feeding stuffs, 71 
Nitrogen, free, not excreted, 202 
Nitrogenous products, excretion of, 140 
Non-nitrogenous matter : 

influence of work on katabolism of, 540 
katabolized in work, nature of, 542 
of urine, 159 
origin of, 160 
Non-proteins, 36 

determination of, in feeding stuffs, 69 
digestion of, 96, 100 
general properties of, 36 
groups of, 36 

indirect utilization of, 622 
influence of, on digestibility, 622 
nitrogen factors for, 70 
occurrence of, 36 
value of, 324, 684 
for maintenance, 324 
Nucleoproteins, 34 

metabolism of, 168 
Nucleus of cells, 42 
Nucleic acids, 34 

digestion of, 99 t 

Nutrients : 
digestible, 599 

computation of, 598 
of metabolizable energy from, 646 



Nutrients, — continued 

net energy values from, 667 
metabolizable energy of, 648 
net energy values of, 668 
significance of, 600 
functions of, 182 
mutual replacement of, 270 
non-nitrogenous, 

effect of deficiency of, 320, 324 

surplus of, 321, 324 
functions of, 187 
physiological functions of, 597 
solution of, in digestion, 101 
Nutrition, balance of, 192, 201 

includes energy, 216 
Nutritive effect, live weight as measure 
of, 196 
total, 195 
Nutritive ratio, 600 

Oat hulls, 584 

Offal, composition of, 55 

proportion of body ash in, 56 
fat in, 56 
protein in, 56 
Oil extraction, by-products of, 586 
Oil meals, 587 

seeds, 581 
Oils, distinction between fats and, 19 

ethereal, 40 
Omasum, 80 
Organic acids, production of in digestion, 

90 
Organic matter, 4 

digestible, computation of metaboliz- 
able energy from, 648 
net energy values from, 673 
subdivision of, 4 
Osmotic pressure, maintenance of, 188 

335 
Outgo of chemical energy, 229 
in cutaneous excretion, 231 
feces, 230 
urine, 231 
heat, 235 

kinetic energy, 235 
work, 235 
Over-all efficiency of body, 562 
Oxygen : 

absorption of, by blood, 13s 

through skin, 139 
consumption of, in metabolism, 146 

determination of, 208 
supply of, 132 
Oxyhemoglobin, 136 



INDEX 



739 



Packing house, by-products of, 590 

Pancreas, 86 

Parotid glands, 79 

Passage of feed from stomach, 83 

Paunch, 80 

Pectins, 15 

Pentosans, 15 

digestion of, 91 

fermentation of, 91 

metabolism of, 158 

proportion of, in crude fiber, 71 
Pentoses, 9 

metabolism of, 158 
Pepsin, 79, 82, 96 
Peptids, 30, 35 
Peptones, 35 
Period system, 477 

Pettenkofer respiration apparatus, 212 
Phosphatids, 22, 23 
Phospholipins, 22 
Phosphoproteins, 35 
Phosphorus : 

anabolism of, 180 

digestion of, 101 

forms of, 7, 180, 421 

inorganic, value of, 421 

katabolism of, 180 

metabolism of, 180 

occurrence of, 7 
Pigs: 

energy requirements of, 400 

feeding standards for, 412 

gains by, in growth, 401 

protein requirements of, 411 
Plane of nutrition, influence of, on energy 
requirements for maintenance, 

305 

milk production, 514 
Plasma, blood, 125 
Polypeptids, 31 
Polysaccharids, n 

chemical structure of, 1 1 

terminology of, 12 
Potassium, metabolism of, 181 

occurrence of, 6 
Power plant, comparison of body with, 

S67 

efficiency of, compared with body, 567 
Practical feeding trials, 592 
Precipitation, shelter from, 456 
Prime motor, animal as, 192 
Production values, 
as regards protein, 678 

energy, 634 
definition of, 630 
3B 



Production values, — continued 
determination of, 630 
of feeding stuffs, 630 ,634, 678 
Prolamins, 33 
Proteans, 35 
Proteases, 79, 86, 87 
Protein : 
addition of, influence of, on digesti- 
bility, 622 
as source of energy, 318, 542 

stimulus to milk glands, 502 
body, fluctuations of, 319 
proportion of, in bone, 48 
offal, 56 
cause of diminished digestibility of, 

619 
cleavage, extent of, in digestion, 98 
computation of gain or loss of, 204 
consumed by calves, 404 

lambs, 407 
crude, determination of, in feeding 
stuffs, 68 
digestibility of, 119 
functions of, in fasting, 255 

work production, 543, 560 
gain of, in fattening, 354 

or loss of, 202 
in dairy rations, 506 
fattening rations, 364 
increase in fattening, 364 
influence of, on digestibility of rations, 

33i 
insufficient, effect of, on growth of 

swine, 409 
katabolism, 

dependent on supply, 322 
in fasting, 251 
variable, 251 
normally small, 251 
in work, influence of non-nitrogenous 

, nutrients on, 538 
influence on, of feed supply, 316 
work, 536 
minimum of, 
for growth, 446 

maintenance, 316, 323 
milk production, 501 
nitrogen factors for, 69 
nutrition, plane of, 324 
of feed, storage of, 319 
optimum of, for maintenance, 323, 330 
physiological minimum of, 254 
production values as regards, 678 
rate of increase of, in growth, 375 
retention of, in growth, 382 



74o 



INDEX 



Protein, — continued 

influence on, of energy supply, 386 
protein supply, 384 
requirements, 

computation of, to unit weight, 325 
for fattening, 363, 416, 446 
growth, 403 
of cattle, 404 
sheep, 407 
swine, 408 
results in practice, 403 
maintenance, 313, 323 

nature of, 313 
meat production, 445 
milk production, 501 
work production, 561 
of cattle, 326, 367, 404, 501 
horses, 329, 561 
sheep, 327, 365, 407 
swine, 329, 368, 408 
relation of, to age, 445 
rich feeds, influence of, on milk pro- 
duction, 506 
supply, influence of, on digestibility, 

447 _ 
milk production, 504, 507 
retention in growth, 384 
surplus, katabolized, 317, 488 
true, determination of, in feeding 

stuffs, 68 
unnecessary for fat production, 363 
utilization of, in fattening, 364 
growth, 384, 387, 388 
milk production, 488, 491 
limited, 318 
Proteins, 24 

alfalfa, values of, 683 
cereal, values of, 683 
chemical changes in resorption of, 107 
coagulated, 35 
coagulation of, 26 
conjugated, 25, 34 
derived, 25, 35 
primary, 35 
secondary, 35 
digestion of, 83, 88, 95 
by erepsin, 98 
•pepsin, 96 
trypsin, 97 
formation of fat from, 173 
functions of, 185 
incomplete, 679 
maize, low value of, 681 
nomenclature of, 24 
of milk, 459 



Proteins, — continued 
origin of, 465 
physical properties of, 25 
putrefaction of, 99 
relative values of, 678 
for growth, 381 
maintenance, 315 
milk production, 492 
simple, 25, 26 
anabolism of, 160 
classification of, 32 
cleavage products of, 28 
composition of, 26 
deaminization of, 165 

reversible, 166 
formation of, 

ammonia in katabolism of, 165 
carbohydrates from, 167 
fat from, 168 
hydrolysis of, 28, 164 
katabolism of, 162 
metabolism of, 160 
• nitrogenous end products of katab- 
olism of, 162 
non-nitrogenous residue of, 163 
proportions of cleavage products in, 

31 
structure of, 27 
synthesis of, 30 

from digestive products, 160 
two stages in katabolism of, 164 
unbalanced, 679 
Proteoses, 35 
Protoplasm, 42 

composition of, 44 
Ptyalin, 78, 79 

conditions of action of, 92 
Pulmonary exchange, investigation of, 

214 
Putrefaction of proteins, 99 
Pylorus, 83 

Quantity of feed, influence of, on diges- 
tibility, 613 
Quotient, respiratory, 207 

Raffinose, n 

Rate of growth, 373 

at different ages, 374 
Rations : 

compounding of, 707 
computation of, 565, 689, 697 
from given feeding stuffs, 700 
improvement of, 698 
for work production, calculation of, 565 



INDEX 



741 



Rectum, 85 

Regnault-Reiset respiration apparatus, 

209 
Relative values of feeding stuffs, 591, 

597 
Requirements : 
for fattening, 350, 359, 361, 363 
growth, 396, 399, 403, 414 
maintenance, 269, 280, 313, 332 
meat production, 444, 445, 448 
milk production, 500, 501, 511, 520 
work production, 560, 562 
of ash, 

for growth, 414 
maintenance, 332 
milk production, 520 
work production, 562 
dry matter, 696 
energy for fattening, 361 
growth, 399 
maintenance, 280, 303 
meat production, 448 
milk production, 511 
work production, 562, 564 
feed, 691, 693, 694 
fat for milk production, 516 
protein for fattening, 363 
growth, 403 
maintenance, 313, 323 
meat production, 445 
milk production, 501 
work production, 561 
Residue, non-nitrogenous, of simple pro- 
teins, 163 
Resorption, 105 

chemical changes in, 107 
mechanism of, 106 
paths of, 107 
role of osmosis in, 106 
Respiration, 123, 132 
apparatus, 208 
Pettenkofer, 212 
Regnault-Reiset, 209 
calorimeters, 236 
influence of work on, 536 
of tissues, 136 
regulation of, 137 
Respiratory quotient, 207 
Reticulum, 80 

Reversible reactions, 150, 166 
Reversibility of metabolic reactions, 152, 

iS3 
Rhamnose, 9 
Rice bran, 583 
polish, 583 



Roots, 73, 579 

influence of, on digestibility, 618 
Roughage, 72, 572 

comparison of, with concentrates, 662 

general character of, 572 

influence of cutting on digestibility of, 

624 
proportion of, to concentrates, 451, 

696 
proportion of vegetative organs in, 
576 
Rumen, 80 

Ruminants, digestibility by, compared 
with horses, 604 
swine, 606 
species of, 603 
net energy values for, 660 
Rumination, 81 
Rye bran, 582 

Saliva, 79 

action of, in stomach, 73 
on starch, 92 
Saponification of fats in digestion, 95 
Schematic body, 195 
Scleroproteins, 34 
Sheep : 

digestibility by, compared with horse, 
604 
swine, 606 
energy requirements for growth, 401 

maintenance, 292 
influence of feed consumption on heat 

production by, 653 
maintenance requirements of, com- 
pared with cattle, 294 
protein requirements for growth, 407 
maintenance, 456 
Shelter from precipitation, 456 
sun, 457 
wind, 456 
influence of, on meat production, 456 
milk production, 484 
Size of animal, influence of, on fasting 

katabolism, 258 
Skeleton as reserve of ash ingredients, 

338 
Skin, gaseous exchange through, 139 
Slaughter tests, comparative, 199, 351 
Sodium, metabolism of, 181 

occurrence of, 6 
Solution of nutrients in digestion, 101 
Species, influence of, on digestibility, 603 

of ruminants, digestibility by, 603 
Specific dynamic action, 275 



742 



INDEX 



Specific effects of feeds, 448 

associated with fats, 527 

on milk production, 523 
Speed, influence of, on efficiency of 
body, 552, 557 

on energy expenditure in locomotion, 

552, 557 
Standing and lying, influence of, on 

fasting katabolism, 261 
Starch, 13 

digestion of, 79, 88, 92 
in intestines, 94 
stomach, 93 
fermentation of, in digestion, 94 
manufacture, by-products of, 587 
values, 672 
Steapsin, 79, 86 
Stomach, 79 
of hog, 81 
horse, 81 
ruminants, 80 
sheep, 80 
passage of feed from, 83 
Straw, 577 
Suckling animals, net energy values for 

growth of, 391 
Sucrase, 79, 87 
Sucrose, 10 
Sugar beet pulp, 589 
Sugar manufacture, by-products of, 588 
Sulphur, 

digestion of, 101 
katabolism of, 179 
metabolism of, 179 
occurrence of, 7 
Sun, shelter from, 457 
Sundry ingredients of animals, 39 

plants, 40 
Surface, computation of, 

computation of katabolism per unit 
of, 258 
Surplus feed, disposal of, 350 
Swine : 

digestibility by, compared with fowls, 
608 
ruminants, 606 
effect of insufficient protein on growth 

of, 409 
energy requirements for growth, 400 

maintenance, 285 
influence of feed consumption on heat 

production by, 653 
net energy values for, 661 
protein requirements for growth, 408 
maintenance, 329 



Synthesis 

of hippuric acid, 163 
nucleic acids, 169 

simple proteins from digestive prod- 
ucts, 160 
seat of, 161 
uric acid, 171 
Synthetic processes in the body, 146 

Tankage, 590 
Temperature, 

body, chemical regulation of, 263 

physical regulation of, 262 
critical, 264, 453 

lowered by feed consumption, 308 
effects of extremes of, 266 
external, influence of age, on effects of, 

454 
amount of ration on effects of, 454 
humidity, on effects of, 455 
live weight on effects of, 454 
influence of, on fasting katabolism, 
262, 265 
energy requirements for mainte- 
nance, 304 
meat production, 453 
milk production, 483 
modifying factors, 484 
of drinking water, influence of, on 

meat production, 455 
relation of, to energy requirements for 
maintenance, 308 
Tendon, 49 
Tissue, adipose, 58 

composition of, 59 
Tissues : 
animal, 45 

classification of, 45 
connective, 49 
elastic, 49 
epidermal, 57 

composition of, 57 
functions of, 57 
of alimentation, 54 

chemical composition of, 55 
motion, 50 
reserve, 58 
supporting, 46 
Tonus, 534 
Total feed required, computation of, 

697 
Training, influence of, on efficiency of 

body, 556 
Triglycerids, 17, 19 

elementary composition of, 20 



INDEX 



743 



Trisaccharids, n 
Trypsin, 79, 86, 97 
Tubers, 73, 579 

influence of, on digestibility, 618 
Type, relation of, to meat production, 
443 

Units of energy, 220 
equivalence of, 221 
Urea, 162 

antecedents of, 162 
Urine, losses of chemical energy in, 636 
non-nitrogenous matter of, 159 

origin of, 160 
outgo of chemical energy in, 231 
Utilization : 

of energy in growth, 390 
milk production, 493 
feed in growth, 381 

milk production, 488 
non-proteins, 686 
proteins, in growth, 384, 387, 388 
milk production, 488 
estimates of, 489, 491 
meaning of, 488 

relative, of fats and carbohydrates for 
work production, 553 

Veins, 126 
Villi, 105 
Vitamins, 41, 348 

Water: 

balance of, 216 

determination of, in feeding stuffs, 

67 
drinking, influence of, on digestibility, 
628 
meat production, 455 
excretion of, 142 
functions of, 3, 190 
supply, 458 
Waxes, 21 

Weight. (See Live weight) 
Wheat bran, 582 
Wind, shelter from, 456 



Work: 

analysis of, 500 

body substance source of energy for, 

544 
forms of, influence of, on efficiency of 

body, 555 
influence of, 

on circulation, 535 
digestibility, 610 
gaseous exchange, 540 
katabolism of non-nitrogenous 
matter, 540 
protein, 536 
respiration, 536 
intensity of, influence of, on efficiency 

of body, 557 
internal, 256 

measure of energy expended in, 
256 
muscular, nature of, 531 
nature of non-nitrogenous matter 

katabolized in, 542 
of ascent, 551 

efficiency of body in, 551 
of digestion, 277 

differences between feeding stuffs, 663 
roughage compared with concentrates, 

662 
draft, 552 

efficiency of body in, 552 
outgo of, 235 

protein as source of energy for, 542 
secondary effects of, 535 
sources of energy for, 542 
Work production, 531 
ash requirements for, 565 
calculation of rations for, 565 
energy requirements for, 562 
feed requirements for, 560 
functions of protein in, 543, 560 
net energy values for, 563 
physiology of, 531 
protein requirements for, 561 

Xylan, 15 
Xylose, 9 



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